zeus
151 lines
4.7 KiB
Swift
151 lines
4.7 KiB
Swift
/// An SQL ordering term.
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///
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/// `SQLOrdering` is an opaque representation of an SQL ordering term.
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/// You generally build `SQLOrdering` from other expressions. For example:
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///
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/// ```swift
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/// Column("score").desc
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/// SQL("score DESC").sqlOrdering
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/// ```
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///
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/// `SQLOrdering` is better used as the return type of a function. For
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/// function arguments, prefer the ``SQLOrderingTerm`` protocol.
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///
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/// Related SQLite documentation: <https://www.sqlite.org/syntax/ordering-term.html>
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public struct SQLOrdering {
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private var impl: Impl
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private enum Impl {
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/// An expression
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///
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/// ORDER BY score
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case expression(SQLExpression)
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/// An ascending expression
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///
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/// ORDER BY score ASC
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case asc(SQLExpression)
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/// An descending expression
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///
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/// ORDER BY score DESC
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case desc(SQLExpression)
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/// Only available from SQLite 3.30.0
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case ascNullsLast(SQLExpression)
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/// Only available from SQLite 3.30.0
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case descNullsFirst(SQLExpression)
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/// A literal SQL ordering
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case literal(SQL)
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}
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static func expression(_ expression: SQLExpression) -> SQLOrdering {
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self.init(impl: .expression(expression))
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}
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static func asc(_ expression: SQLExpression) -> SQLOrdering {
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self.init(impl: .asc(expression))
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}
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static func desc(_ expression: SQLExpression) -> SQLOrdering {
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self.init(impl: .desc(expression))
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}
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static func ascNullsLast(_ expression: SQLExpression) -> SQLOrdering {
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self.init(impl: .ascNullsLast(expression))
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}
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static func descNullsFirst(_ expression: SQLExpression) -> SQLOrdering {
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self.init(impl: .descNullsFirst(expression))
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}
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static func literal(_ sqlLiteral: SQL) -> SQLOrdering {
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self.init(impl: .literal(sqlLiteral))
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}
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}
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extension SQLOrdering {
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func sql(_ context: SQLGenerationContext) throws -> String {
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switch impl {
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case .expression(let expression):
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return try expression.sql(context)
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case .asc(let expression):
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return try expression.sql(context) + " ASC"
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case .desc(let expression):
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return try expression.sql(context) + " DESC"
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case .ascNullsLast(let expression):
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return try expression.sql(context) + " ASC NULLS LAST"
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case .descNullsFirst(let expression):
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return try expression.sql(context) + " DESC NULLS FIRST"
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case .literal(let literal):
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return try literal.sql(context)
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}
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}
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}
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extension SQLOrdering {
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func qualified(with alias: TableAlias) -> SQLOrdering {
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switch impl {
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case .expression(let expression):
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return .expression(expression.qualified(with: alias))
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case .asc(let expression):
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return .asc(expression.qualified(with: alias))
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case .desc(let expression):
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return .desc(expression.qualified(with: alias))
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case .ascNullsLast(let expression):
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return .ascNullsLast(expression.qualified(with: alias))
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case .descNullsFirst(let expression):
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return .descNullsFirst(expression.qualified(with: alias))
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case .literal(let literal):
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return .literal(literal.qualified(with: alias))
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}
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}
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}
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extension SQLOrdering {
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var reversed: SQLOrdering {
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switch impl {
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case .expression(let expression):
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return .desc(expression)
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case .asc(let expression):
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return .desc(expression)
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case .desc(let expression):
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return .asc(expression)
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case .ascNullsLast(let expression):
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return .descNullsFirst(expression)
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case .descNullsFirst(let expression):
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return .ascNullsLast(expression)
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case .literal:
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fatalError("""
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Ordering literals can't be reversed. \
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To resolve this error, order by expression literals instead. \
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For example: order(SQL("(score + bonus)").sqlExpression)
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""")
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}
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}
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}
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// MARK: - SQLOrderingTerm
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/// A type that can be used as an SQL ordering term.
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///
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/// Related SQLite documentation <https://www.sqlite.org/syntax/ordering-term.html>
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///
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/// ## Topics
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///
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/// ### Supporting Type
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///
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/// - ``SQLOrdering``
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public protocol SQLOrderingTerm {
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/// Returns an SQL ordering.
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var sqlOrdering: SQLOrdering { get }
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}
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extension SQLOrdering: SQLOrderingTerm {
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// Not a real deprecation, just a usage warning
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@available(*, deprecated, message: "Already QLOrdering:")
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public var sqlOrdering: SQLOrdering { self }
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}
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