zeus
568 lines
20 KiB
Swift
568 lines
20 KiB
Swift
/// SQLGenerationContext supports SQL generation:
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///
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/// - It provides a database connection during SQL generation, for any purpose
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/// such as schema introspection.
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///
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/// - It provides unique table aliases in order to disambiguates table names
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/// and columns.
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///
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/// - It gathers SQL arguments in order to prevent SQL injection.
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final class SQLGenerationContext {
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private enum Parent {
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case none(db: Database, argumentsSink: StatementArgumentsSink)
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case context(SQLGenerationContext)
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}
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/// A database connection.
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var db: Database {
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switch parent {
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case let .none(db: db, argumentsSink: _): return db
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case let .context(context): return context.db
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}
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}
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/// All gathered arguments
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var arguments: StatementArguments { argumentsSink.arguments }
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/// Access to the database connection, the arguments sink, ctes, and resolved
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/// names of table aliases from outer contexts (useful in case of
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/// subquery generation).
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private let parent: Parent
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/// The arguments sink which prevents SQL injection.
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private var argumentsSink: StatementArgumentsSink {
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switch parent {
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case let .none(db: _, argumentsSink: argumentsSink): return argumentsSink
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case let .context(context): return context.argumentsSink
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}
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}
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private let resolvedNames: [TableAlias: String]
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private let ownAliases: Set<TableAlias>
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private let ownCTEs: [String: SQLCTE]
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/// Creates a generation context.
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///
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/// - parameter db: A database connection.
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/// - parameter argumentsSink: An arguments sink.
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/// - parameter aliases: An array of table aliases to disambiguate.
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/// - parameter ctes: An dictionary of available CTEs.
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init(
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_ db: Database,
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argumentsSink: StatementArgumentsSink = StatementArgumentsSink(),
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aliases: [TableAlias] = [],
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ctes: OrderedDictionary<String, SQLCTE> = [:])
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{
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self.parent = .none(db: db, argumentsSink: argumentsSink)
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self.resolvedNames = aliases.resolvedNames
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self.ownAliases = Set(aliases)
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self.ownCTEs = Dictionary(uniqueKeysWithValues: ctes.lazy.map { ($0.lowercased(), $1) })
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}
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/// Creates a generation context.
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///
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/// - parameter parent: A parent context.
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/// - parameter aliases: An array of table aliases to disambiguate.
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/// - parameter ctes: An dictionary of available CTEs.
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private init(
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parent: SQLGenerationContext,
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aliases: [TableAlias],
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ctes: OrderedDictionary<String, SQLCTE>)
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{
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self.parent = .context(parent)
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self.resolvedNames = aliases.resolvedNames
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self.ownAliases = Set(aliases)
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self.ownCTEs = Dictionary(uniqueKeysWithValues: ctes.lazy.map { ($0.lowercased(), $1) })
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}
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/// Returns a generation context suitable for subqueries.
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func subqueryContext(
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aliases: [TableAlias] = [],
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ctes: OrderedDictionary<String, SQLCTE> = [:]) -> SQLGenerationContext
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{
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SQLGenerationContext(parent: self, aliases: aliases, ctes: ctes)
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}
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/// Returns whether arguments could be appended.
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///
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/// A false result means that the generation context does not support
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/// SQL arguments, and `?` placeholders are not supported.
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/// This happens, for example, when we are creating tables:
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///
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/// // CREATE TABLE player (
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/// // name TEXT DEFAULT 'Anonymous' -- String literal instead of ?
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/// // )
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/// let defaultName = "Anonymous"
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/// try db.create(table: "player") { t in
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/// t.column(literal: "name TEXT DEFAULT \(defaultName)")
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/// }
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///
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/// A false result is turned into a fatal error when the user uses
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/// SQL arguments at unsupported locations:
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///
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/// // Fatal error:
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/// // Not implemented: turning an SQL parameter into an SQL literal value
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/// let defaultName = "Anonymous"
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/// let literal = SQL(sql: "name TEXT DEFAULT ?", arguments: [defaultName])
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/// try db.create(table: "player") { t in
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/// t.column(literal: literal)
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/// }
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func append(arguments: StatementArguments) -> Bool {
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argumentsSink.append(arguments: arguments)
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}
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/// May be nil, when a qualifier is not needed:
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///
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/// WHERE <qualifier>.column == 1
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/// SELECT <qualifier>.*
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///
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/// WHERE column == 1
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/// SELECT *
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func qualifier(for alias: TableAlias) -> String? {
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if alias.hasUserName {
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return alias.identityName
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}
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if !ownAliases.contains(alias) {
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return resolvedName(for: alias)
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}
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if ownAliases.count > 1 {
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return resolvedName(for: alias)
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}
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return nil
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}
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/// WHERE <resolvedName> MATCH pattern
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func resolvedName(for alias: TableAlias) -> String {
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if let name = resolvedNames[alias] {
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return name
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}
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switch parent {
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case .none:
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return alias.identityName
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case let .context(context):
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return context.resolvedName(for: alias)
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}
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}
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/// FROM tableName <alias>
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func aliasName(for alias: TableAlias) -> String? {
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let resolvedName = self.resolvedName(for: alias)
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if resolvedName != alias.tableName {
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return resolvedName
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}
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return nil
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}
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func columnCount(in tableName: String) throws -> Int {
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if let cte = ownCTEs[tableName.lowercased()] {
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return try cte.columnCount(db)
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}
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switch parent {
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case let .context(context):
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return try context.columnCount(in: tableName)
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case let .none(db: db, argumentsSink: _):
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return try db.columns(in: tableName).count
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}
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}
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}
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/// A class that gathers statement arguments, and can be shared between
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/// several SQLGenerationContext.
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class StatementArgumentsSink {
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private(set) var arguments: StatementArguments
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private let rawSQL: Bool
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/// A sink which turns all argument values into SQL literals.
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///
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/// The `"WHERE name = \("O'Brien")"` SQL literal is turned into the
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/// `WHERE name = 'O''Brien'` SQL.
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static let literalValues = StatementArgumentsSink(rawSQL: true)
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private init(rawSQL: Bool) {
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self.arguments = []
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self.rawSQL = rawSQL
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}
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/// A sink which turns all argument values into `?` SQL parameters.
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///
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/// The `"WHERE name = \("O'Brien")"` SQL literal is turned into the
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/// `WHERE name = ?` SQL.
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convenience init() {
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self.init(rawSQL: false)
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}
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// fileprivate so that SQLGenerationContext.append(arguments:) is the only
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// available api.
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/// Returns false for SQLGenerationContext.rawSQLContext
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fileprivate func append(arguments: StatementArguments) -> Bool {
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if arguments.isEmpty {
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return true
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}
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if rawSQL {
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return false
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}
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self.arguments += arguments
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return true
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}
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}
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// MARK: - TableAlias
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/// A TableAlias identifies a table in a request.
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///
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/// See ``TableRequest/aliased(_:)`` for more information and examples.
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///
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/// - note: [**🔥 EXPERIMENTAL**](https://github.com/groue/GRDB.swift/blob/master/README.md#what-are-experimental-features)
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public class TableAlias {
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private enum Impl {
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/// A TableAlias is undefined when it is created by the GRDB user:
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///
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/// let alias = TableAlias()
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/// let alias = TableAlias(name: "custom")
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case undefined(userName: String?)
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/// A TableAlias is a table when explicitly specified:
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///
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/// let alias = TableAlias(tableName: "player")
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///
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/// Or when it qualifies a request that wasn't qualified yet (in which
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/// case it turns from undefined to a table):
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///
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/// // SELECT custom.* FROM player custom
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/// let alias = TableAlias(name: "custom")
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/// let request = Player.all().aliased(alias)
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case table(tableName: String, userName: String?)
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/// A TableAlias can be a proxy for another table alias. Two different
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/// instances for the same table identifier:
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///
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/// // Pointless example: make alias2 a proxy for alias1
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/// let alias1 = TableAlias()
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/// let alias2 = TableAlias()
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/// Player.all()
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/// .aliased(alias1)
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/// .aliased(alias2)
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///
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/// Proxies are useful because queries get implicit aliases as soon
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/// as they are joined with associations. In the example below,
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/// customAlias becomes a proxy for the request's implicit alias, which
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/// gets a custom name. This allows implicit and user aliases to merge
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/// into a single "table identifier" that matches the user's expectations:
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///
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/// // SELECT custom.*, team.*
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/// // FROM player custom
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/// // JOIN team ON taem.id = custom.teamId
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/// // WHERE custom.name = 'Arthur'
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/// let customAlias = TableAlias(name: "custom")
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/// let request = Player
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/// .including(required: Player.team)
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/// .filter(sql: "custom.name = 'Arthur'")
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/// .aliased(customAlias)
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case proxy(TableAlias)
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}
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private var impl: Impl
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/// Resolve all proxies
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private var root: TableAlias {
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if case .proxy(let base) = impl {
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return base.root
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} else {
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return self
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}
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}
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// exposed to SQLGenerationContext
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fileprivate var identityName: String {
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userName ?? tableName
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}
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// exposed to SQLGenerationContext
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fileprivate var hasUserName: Bool {
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userName != nil
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}
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var tableName: String {
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switch impl {
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case .undefined:
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// Likely a GRDB bug
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fatalError("Undefined alias has no table name")
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case .table(tableName: let tableName, userName: _):
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return tableName
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case .proxy(let base):
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return base.tableName
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}
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}
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private var userName: String? {
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switch impl {
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case .undefined(let userName):
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return userName
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case .table(tableName: _, userName: let userName):
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return userName
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case .proxy(let base):
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return base.userName
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}
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}
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/// Creates a TableAlias.
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///
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/// When the alias is given a name, this name is guaranteed to be used as
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/// the table alias in the SQL query:
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///
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/// ```swift
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/// // SELECT p.* FROM player p
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/// let alias = TableAlias(name: "p")
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/// let request = Player.all().aliased(alias)
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/// ```
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public init(name: String? = nil) {
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self.impl = .undefined(userName: name)
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}
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init(tableName: String, userName: String? = nil) {
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self.impl = .table(tableName: tableName, userName: userName)
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}
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func becomeProxy(of base: TableAlias) {
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if self === base {
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return
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}
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switch impl {
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case let .undefined(userName):
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if let userName {
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// rename
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assert(base.userName == nil || base.userName == userName)
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base.setUserName(userName)
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}
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self.impl = .proxy(base)
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case let .table(tableName: tableName, userName: userName):
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assert(tableName == base.tableName)
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if let userName {
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// rename
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assert(base.userName == nil || base.userName == userName)
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base.setUserName(userName)
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}
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self.impl = .proxy(base)
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case let .proxy(selfBase):
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selfBase.becomeProxy(of: base)
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}
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}
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/// Returns nil if aliases can't be merged (conflict in tables, aliases...)
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func merged(with other: TableAlias) -> TableAlias? {
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if self === other {
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return self
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}
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let root = self.root
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let otherRoot = other.root
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switch (root.impl, otherRoot.impl) {
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case let (.table(tableName: tableName, userName: userName),
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.table(tableName: otherTableName, userName: otherUserName)):
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guard tableName == otherTableName else {
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// can't merge
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return nil
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}
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if let userName, let otherUserName, userName != otherUserName {
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// can't merge
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return nil
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}
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root.becomeProxy(of: otherRoot)
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return otherRoot
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default:
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// can't merge
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return nil
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}
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}
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private func setUserName(_ userName: String) {
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switch impl {
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case .undefined:
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self.impl = .undefined(userName: userName)
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case .table(tableName: let tableName, userName: _):
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self.impl = .table(tableName: tableName, userName: userName)
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case .proxy(let base):
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base.setUserName(userName)
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}
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}
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func setTableName(_ tableName: String) {
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switch impl {
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case .undefined(let userName):
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self.impl = .table(tableName: tableName, userName: userName)
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case .table(tableName: let initialTableName, userName: _):
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// It is a programmer error to reuse the same TableAlias for
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// multiple tables.
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//
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// // Don't do that
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// let alias = TableAlias()
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// let books = Book.aliased(alias)...
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// let authors = Author.aliased(alias)...
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GRDBPrecondition(
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tableName.lowercased() == initialTableName.lowercased(),
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"A TableAlias most not be used to refer to multiple tables")
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case .proxy(let base):
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base.setTableName(tableName)
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}
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}
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/// Returns a result column that refers to the aliased table.
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public subscript(_ selectable: some SQLSelectable) -> SQLSelection {
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// TODO: test
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selectable.sqlSelection.qualified(with: self)
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}
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/// Returns an SQL expression that refers to the aliased table.
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///
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/// For example, let's sort books by author name first, and then by title:
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///
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/// ```swift
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/// // SELECT book.*
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/// // FROM book
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/// // JOIN author ON author.id = book.authorId
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/// // ORDER BY author.name, book.title
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/// let authorAlias = TableAlias()
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/// let request = Book
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/// .joining(required: Book.author.aliased(authorAlias))
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/// .order(authorAlias[Column("name")], Column("title"))
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/// ```
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public subscript(_ expression: some SQLSpecificExpressible & SQLSelectable & SQLOrderingTerm) -> SQLExpression {
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expression.sqlExpression.qualified(with: self)
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}
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public subscript(_ expression: some SQLJSONExpressible &
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SQLSpecificExpressible &
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SQLSelectable &
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SQLOrderingTerm)
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-> AnySQLJSONExpressible
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{
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AnySQLJSONExpressible(sqlExpression: expression.sqlExpression.qualified(with: self))
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}
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/// Returns an SQL ordering term that refers to the aliased table.
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///
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/// For example, let's sort books by author name first, and then by title:
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///
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/// ```swift
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/// // SELECT book.*
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/// // FROM book
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/// // JOIN author ON author.id = book.authorId
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/// // ORDER BY author.name ASC, book.title ASC
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/// let authorAlias = TableAlias()
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/// let request = Book
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/// .joining(required: Book.author.aliased(authorAlias))
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/// .order(authorAlias[Column("name").asc], Column("title").asc)
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/// ```
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public subscript(_ ordering: some SQLOrderingTerm) -> SQLOrdering {
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ordering.sqlOrdering.qualified(with: self)
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}
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/// Returns an SQL column that refers to the aliased table.
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///
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/// For example, let's sort books by author name first, and then by title:
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///
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/// ```swift
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/// // SELECT book.*
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/// // FROM book
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/// // JOIN author ON author.id = book.authorId
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/// // ORDER BY author.name, book.title
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/// let authorAlias = TableAlias()
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/// let request = Book
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/// .joining(required: Book.author.aliased(authorAlias))
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/// .order(authorAlias["name"], Column("title"))
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/// ```
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public subscript(_ column: String) -> SQLExpression {
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.qualifiedColumn(column, self)
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}
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/// A boolean SQL expression indicating whether this alias refers to some
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/// rows, or not.
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///
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/// - note: [**🔥 EXPERIMENTAL**](https://github.com/groue/GRDB.swift/blob/master/README.md#what-are-experimental-features)
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///
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/// In the example below, we only fetch books that are not associated to
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/// any author:
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///
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/// ```swift
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/// struct Author: TableRecord, FetchableRecord { }
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/// struct Book: TableRecord, FetchableRecord {
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/// static let author = belongsTo(Author.self)
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/// }
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///
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/// try dbQueue.read { db in
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/// let authorAlias = TableAlias()
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/// let request = Book
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/// .joining(optional: Book.author.aliased(authorAlias))
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/// .filter(!authorAlias.exists)
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/// let books = try request.fetchAll(db)
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/// }
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/// ```
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public var exists: SQLExpression {
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SQLExpression.qualifiedExists(self)
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}
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}
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extension TableAlias: Equatable {
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public static func == (lhs: TableAlias, rhs: TableAlias) -> Bool {
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ObjectIdentifier(lhs.root) == ObjectIdentifier(rhs.root)
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}
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}
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extension TableAlias: Hashable {
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public func hash(into hasher: inout Hasher) {
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hasher.combine(ObjectIdentifier(root))
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}
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}
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extension [TableAlias] {
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/// Resolve ambiguities in aliases' names.
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fileprivate var resolvedNames: [TableAlias: String] {
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// It is a programmer error to reuse the same TableAlias for
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// multiple tables.
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//
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// // Don't do that
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// let alias = TableAlias()
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// let request = Book
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// .including(required: Book.author.aliased(alias)...)
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// .including(required: Book.author.aliased(alias)...)
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GRDBPrecondition(count == Set(self).count, "A TableAlias most not be used to refer to multiple tables")
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let groups = Dictionary(grouping: self) {
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$0.identityName.lowercased()
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}
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var uniqueLowercaseNames: Set<String> = []
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var ambiguousGroups: [[TableAlias]] = []
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for (lowercaseName, group) in groups {
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if group.count > 1 {
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// It is a programmer error to reuse the same alias for multiple tables
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GRDBPrecondition(
|
|
group.countElements(where: \.hasUserName) < 2,
|
|
"ambiguous alias: \(group[0].identityName)")
|
|
ambiguousGroups.append(group)
|
|
} else {
|
|
uniqueLowercaseNames.insert(lowercaseName)
|
|
}
|
|
}
|
|
|
|
var resolvedNames: [TableAlias: String] = [:]
|
|
for group in ambiguousGroups {
|
|
var index = 1
|
|
for alias in group {
|
|
if alias.hasUserName { continue }
|
|
let radical = alias.identityName.digitlessRadical
|
|
var resolvedName: String
|
|
repeat {
|
|
resolvedName = "\(radical)\(index)"
|
|
index += 1
|
|
} while uniqueLowercaseNames.contains(resolvedName.lowercased())
|
|
uniqueLowercaseNames.insert(resolvedName.lowercased())
|
|
resolvedNames[alias] = resolvedName
|
|
}
|
|
}
|
|
return resolvedNames
|
|
}
|
|
}
|