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SQLQueryGenerator.swift
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SQLQueryGenerator.swift
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/// SQLQueryGenerator is able to generate an SQL SELECT query.
struct SQLQueryGenerator: Refinable {
fileprivate private(set) var relation: SQLQualifiedRelation
private let singleResult: Bool
// For database region
private let prefetchedAssociations: [_SQLAssociation]
/// Creates an SQL query generator.
///
/// - parameter singleResult: A hint as to whether the query should be
/// optimized for a single result.
init(
relation: SQLRelation,
forSingleResult singleResult: Bool = false)
{
self.relation = SQLQualifiedRelation(relation)
self.prefetchedAssociations = relation.prefetchedAssociations
self.singleResult = singleResult
}
func requestSQL(_ context: SQLGenerationContext) throws -> String {
let context = context.subqueryContext(aliases: relation.allAliases, ctes: relation.ctes)
var sql = try commonTableExpressionsPrefix(context)
sql += "SELECT"
if relation.isDistinct {
sql += " DISTINCT"
}
let selection = try relation.selectionPromise.resolve(context.db)
GRDBPrecondition(!selection.isEmpty, "Can't generate SQL with an empty selection")
sql += " "
sql += try selection
.map { try $0.sql(context) }
.joined(separator: ", ")
sql += " FROM "
sql += try relation.source.sql(context)
if relation.joins.isEmpty == false {
let sourceAlias = relation.source.alias
for (_, join) in relation.joins {
sql += " "
sql += try join.sql(context, leftAlias: sourceAlias)
}
}
let filter = try relation.filterPromise?.resolve(context.db)
if let filter = filter {
sql += " WHERE "
sql += try filter.sql(context)
}
let groupExpressions = try relation.groupPromise?.resolve(context.db) ?? []
if !groupExpressions.isEmpty {
sql += " GROUP BY "
sql += try groupExpressions
.map { try $0.sql(context) }
.joined(separator: ", ")
}
if let havingExpression = try relation.havingExpressionPromise?.resolve(context.db) {
sql += " HAVING "
sql += try havingExpression.sql(context)
}
let orderings = try relation.ordering.resolve(context.db)
if !orderings.isEmpty {
sql += " ORDER BY "
sql += try orderings
.map { try $0.sql(context) }
.joined(separator: ", ")
}
var limit = relation.limit
if try limit == nil && singleResult && !expectsSingleResult(
context.db,
selection: selection,
filter: filter,
groupExpressions: groupExpressions)
{
limit = SQLLimit(limit: 1, offset: limit?.offset)
}
if let limit = limit {
sql += " LIMIT "
sql += limit.sql
}
return sql
}
func makePreparedRequest(_ db: Database) throws -> PreparedRequest {
try PreparedRequest(
statement: makeStatement(db),
adapter: rowAdapter(SQLGenerationContext(db, ctes: relation.ctes)))
}
/// The number of fetched columns.
func columnCount(_ db: Database) throws -> Int {
try relation
.selectionPromise
.resolve(db)
.columnCount(SQLGenerationContext(db, ctes: relation.ctes))
}
/// Returns a prepared statement
func makeStatement(_ db: Database) throws -> Statement {
// Build
let context = SQLGenerationContext(db)
let sql = try requestSQL(context)
// Compile & set arguments
let statement = try db.makeStatement(sql: sql)
statement.arguments = context.arguments
// Optimize statement region. This allows us to track individual rowids,
// and also find some provably empty requests such as `Player.none()`.
statement.databaseRegion = try optimizedSelectedRegion(db, statement.databaseRegion)
if !statement.databaseRegion.isEmpty {
// Unless the statement region is provably empty, also append the
// region of prefetched associations.
//
// This makes sure we observe the correct database region when the
// statement is executed, even if we don't actually fetch prefetched
// associations, due to lacking database content.
//
// For example, fetching `parent.including(all: children)` will
// select parents, but won't attempt to select any children if there
// is no parent in the database. And yet we need to observe the
// table for children. This is why we include the prefetched region.
//
// Note that the request `parent.none().including(all: children)` is
// different. Since `parent.none()` is provably empty, its region
// is empty, and we thus avoid this code branch.
let region = try prefetchedRegion(
db,
associations: prefetchedAssociations,
from: relation.source.tableName)
statement.databaseRegion.formUnion(region)
}
return statement
}
private func optimizedSelectedRegion(_ db: Database, _ selectedRegion: DatabaseRegion) throws -> DatabaseRegion {
// Can we intersect the region with rowIds?
//
// Give up unless request feeds from a single database table
let tableName = relation.source.tableName
guard try db.tableExists(tableName) else { // skip views
return selectedRegion
}
// The filter knows better
guard let filter = try relation.filterPromise?.resolve(db),
let rowIDs = try filter.identifyingRowIDs(db, for: relation.source.alias)
else {
return selectedRegion
}
return selectedRegion.tableIntersection(tableName, rowIds: rowIDs)
}
/// If true, executing this query yields at most one row.
/// If false, we don't know how many rows this query returns.
private func expectsSingleResult(
_ db: Database,
selection: [SQLSelection],
filter: SQLExpression?,
groupExpressions: [SQLExpression])
throws -> Bool
{
if relation.joins.isEmpty == false {
// Don't expect single results as soon as there is a join
return false
}
// Do we filter on a unique key?
let tableName = relation.source.tableName
if try db.tableExists(tableName), // skip views
let identifyingColums = try filter?.identifyingColums(db, for: relation.source.alias),
try db.table(tableName, hasUniqueKey: identifyingColums)
{
// Filter by unique key: guaranteed single row!
return true
}
// Do we aggregate without grouping?
if groupExpressions.isEmpty && selection.contains(where: \.isAggregate) {
// Selection contains an aggregate function: guaranteed single row!Ë
return true
}
return false
}
func makeDeleteStatement(_ db: Database) throws -> Statement {
switch try grouping(db) {
case .none:
guard relation.joins.isEmpty else {
return try makeTrivialDeleteStatement(db)
}
let context = SQLGenerationContext(db, aliases: relation.allAliases, ctes: relation.ctes)
var sql = try commonTableExpressionsPrefix(context)
sql += try "DELETE FROM " + relation.source.sql(context)
if let filter = try relation.filterPromise?.resolve(db) {
sql += " WHERE "
sql += try filter.sql(context)
}
if let limit = relation.limit {
let orderings = try relation.ordering.resolve(db)
if !orderings.isEmpty {
sql += " ORDER BY "
sql += try orderings
.map { try $0.sql(context) }
.joined(separator: ", ")
}
sql += " LIMIT " + limit.sql
}
let statement = try db.makeStatement(sql: sql)
statement.arguments = context.arguments
return statement
case .unique:
return try makeTrivialDeleteStatement(db)
case .nonUnique:
// Programmer error
fatalError("Can't delete query with GROUP BY clause")
}
}
/// DELETE FROM table WHERE id IN (SELECT id FROM table ...)
private func makeTrivialDeleteStatement(_ db: Database) throws -> Statement {
let tableName = relation.source.tableName
let alias = TableAlias(tableName: tableName)
let context = SQLGenerationContext(db, aliases: [alias])
let subqueryContext = context.subqueryContext(aliases: relation.allAliases, ctes: relation.ctes)
let primaryKey = SQLExpression.fastPrimaryKey
let selectPrimaryKey = self.with {
$0.relation = $0.relation.selectOnly([.expression(primaryKey)])
}
var sql = "DELETE FROM \(tableName.quotedDatabaseIdentifier) WHERE "
sql += try alias[primaryKey].sql(context)
sql += " IN ("
sql += try selectPrimaryKey.requestSQL(subqueryContext)
sql += ")"
let statement = try db.makeStatement(sql: sql)
statement.arguments = context.arguments
return statement
}
/// Returns nil if assignments is empty
func makeUpdateStatement(
_ db: Database,
conflictResolution: Database.ConflictResolution,
assignments: [ColumnAssignment])
throws -> Statement?
{
switch try grouping(db) {
case .none:
guard relation.joins.isEmpty else {
return try makeTrivialUpdateStatement(
db,
conflictResolution: conflictResolution,
assignments: assignments)
}
// Check for empty assignments after all programmer errors have
// been checked.
if assignments.isEmpty {
return nil
}
let context = SQLGenerationContext(db, aliases: relation.allAliases, ctes: relation.ctes)
var sql = try commonTableExpressionsPrefix(context)
sql += "UPDATE "
if conflictResolution != .abort {
sql += "OR \(conflictResolution.rawValue) "
}
sql += try relation.source.sql(context)
sql += " SET "
sql += try assignments
.map { try $0.sql(context) }
.joined(separator: ", ")
if let filter = try relation.filterPromise?.resolve(db) {
sql += " WHERE "
sql += try filter.sql(context)
}
if let limit = relation.limit {
let orderings = try relation.ordering.resolve(db)
if !orderings.isEmpty {
sql += " ORDER BY "
sql += try orderings
.map { try $0.sql(context) }
.joined(separator: ", ")
}
sql += " LIMIT " + limit.sql
}
let statement = try db.makeStatement(sql: sql)
statement.arguments = context.arguments
return statement
case .unique:
return try makeTrivialUpdateStatement(db, conflictResolution: conflictResolution, assignments: assignments)
case .nonUnique:
// Programmer error
fatalError("Can't update query with GROUP BY clause")
}
}
/// UPDATE table SET ... WHERE id IN (SELECT id FROM table ...)
/// Returns nil if assignments is empty
private func makeTrivialUpdateStatement(
_ db: Database,
conflictResolution: Database.ConflictResolution,
assignments: [ColumnAssignment])
throws -> Statement?
{
// Check for empty assignments after all programmer errors have
// been checked.
if assignments.isEmpty {
return nil
}
let tableName = relation.source.tableName
let alias = TableAlias(tableName: tableName)
let context = SQLGenerationContext(db, aliases: [alias])
let subqueryContext = context.subqueryContext(aliases: relation.allAliases, ctes: relation.ctes)
let primaryKey = SQLExpression.fastPrimaryKey
let selectPrimaryKey = self.with {
$0.relation = $0.relation.selectOnly([.expression(primaryKey)])
}
// UPDATE table...
var sql = "UPDATE "
if conflictResolution != .abort {
sql += "OR \(conflictResolution.rawValue) "
}
sql += tableName.quotedDatabaseIdentifier
// SET column = value...
sql += " SET "
sql += try assignments
.map { try $0.sql(context) }
.joined(separator: ", ")
// WHERE id IN (SELECT id FROM ...)
sql += " WHERE "
sql += try alias[primaryKey].sql(context)
sql += " IN ("
sql += try selectPrimaryKey.requestSQL(subqueryContext)
sql += ")"
let statement = try db.makeStatement(sql: sql)
statement.arguments = context.arguments
return statement
}
private func commonTableExpressionsPrefix(_ context: SQLGenerationContext) throws -> String {
if relation.ctes.isEmpty {
return ""
}
var sql = "WITH "
if relation.ctes.values.contains(where: \.isRecursive) {
sql += "RECURSIVE "
}
sql += try relation.ctes
.map { tableName, cte in
var columnsSQL = ""
if let columns = cte.columns, !columns.isEmpty {
columnsSQL = "("
columnsSQL += columns
.map(\.quotedDatabaseIdentifier)
.joined(separator: ", ")
columnsSQL += ")"
}
let cteContext = context.subqueryContext()
let subquerySQL = try cte.sqlSubquery.sql(cteContext)
return "\(tableName.quotedDatabaseIdentifier)\(columnsSQL) AS (\(subquerySQL))"
}
.joined(separator: ", ")
sql += " "
return sql
}
/// Informs about the query grouping
private enum GroupingInfo {
/// No grouping at all: SELECT ... FROM player
case none
/// Grouped by unique key: SELECT ... FROM player GROUP BY id
case unique
/// Grouped by some non-unique columnns: SELECT ... FROM player GROUP BY teamId
case nonUnique
}
/// Informs about the query grouping
private func grouping(_ db: Database) throws -> GroupingInfo {
// Empty group clause: no grouping
// SELECT * FROM player
guard let groupExpressions = try relation.groupPromise?.resolve(db), groupExpressions.isEmpty == false else {
return .none
}
// Grouping something which is not a table: assume non unique grouping.
let tableName = relation.source.tableName
guard try db.tableExists(tableName) else { // skip views
return .nonUnique
}
var groupingColumns: Set<String> = []
for expression in groupExpressions {
guard let column = try expression.column(db, for: relation.source.alias, acceptsBijection: true) else {
// Grouping by something which is not a column: assume non
// unique grouping.
return .nonUnique
}
groupingColumns.insert(column)
}
// Grouping by some column(s) which are unique
// SELECT * FROM player GROUP BY id
if try db.table(tableName, hasUniqueKey: groupingColumns) {
return .unique
}
// Grouping by some column(s) which are not unique
// SELECT * FROM player GROUP BY score
return .nonUnique
}
/// Returns the row adapter which presents the fetched rows according to the
/// tree of joined relations.
///
/// The adapter is nil for queries without any included relation,
/// because the fetched rows don't need any processing:
///
/// // SELECT * FROM book
/// let request = Book.all()
/// for row in try Row.fetchAll(db, request) {
/// row // [id:1, title:"Moby-Dick"]
/// let book = Book(row: row)
/// }
///
/// But as soon as the selection includes columns of a included relation,
/// we need an adapter:
///
/// // SELECT book.*, author.* FROM book JOIN author ON author.id = book.authorId
/// let request = Book.including(required: Book.author)
/// for row in try Row.fetchAll(db, request) {
/// row // [id:1, title:"Moby-Dick"]
/// let book = Book(row: row)
///
/// row.scopes["author"] // [id:12, name:"Herman Melville"]
/// let author: Author = row["author"]
/// }
private func rowAdapter(_ context: SQLGenerationContext) throws -> RowAdapter? {
try relation.rowAdapter(context, fromIndex: 0, rootRelation: true)?.adapter
}
}
/// To generate SQL, we need a "qualified" relation, where all tables,
/// expressions, etc, are qualified with table aliases.
///
/// All those aliases let us disambiguate tables at the SQL level, and
/// prefix columns names. For example, the following request...
///
/// Book.filter(Column("kind") == Book.Kind.novel)
/// .including(optional: Book.author)
/// .including(optional: Book.translator)
/// .annotated(with: Book.awards.count)
///
/// ... generates the following SQL, where all identifiers are correctly
/// disambiguated and qualified:
///
/// SELECT book.*, person1.*, person2.*, COUNT(DISTINCT award.id)
/// FROM book
/// LEFT JOIN person person1 ON person1.id = book.authorId
/// LEFT JOIN person person2 ON person2.id = book.translatorId
/// LEFT JOIN award ON award.bookId = book.id
/// GROUP BY book.id
/// WHERE book.kind = 'novel'
///
/// `SQLQualifiedRelation` contains the following information:
///
/// WITH ... -- ctes
/// SELECT ... -- selectionPromise
/// FROM ... -- source
/// JOIN ... -- joins
/// WHERE ... -- filterPromise
/// GROUP BY ... -- groupPromise
/// HAVING ... -- havingExpressionPromise
/// ORDER BY ... -- ordering
/// LIMIT ... -- limit
private struct SQLQualifiedRelation {
/// All aliases, including aliases of joined relations
var allAliases: [TableAlias] {
joins.reduce(into: [source.alias].compactMap { $0 }) {
$0.append(contentsOf: $1.value.relation.allAliases)
}
}
/// The source
let source: SQLQualifiedSource
/// The selection from source, not including selection of joined relations
private var sourceSelectionPromise: DatabasePromise<[SQLSelection]>
var isDistinct: Bool
/// The full selection, including selection of joined relations
var selectionPromise: DatabasePromise<[SQLSelection]> {
DatabasePromise { db in
let selection = try self.sourceSelectionPromise.resolve(db)
return try self.joins.values.reduce(into: selection) { selection, join in
let joinedSelection = try join.relation.selectionPromise.resolve(db)
selection.append(contentsOf: joinedSelection)
}
}
}
let filterPromise: DatabasePromise<SQLExpression>?
/// The ordering of source, not including ordering of joined relations
private let sourceOrdering: SQLRelation.Ordering
/// The full ordering, including orderings of joined relations
var ordering: SQLRelation.Ordering {
joins.reduce(sourceOrdering) {
$0.appending($1.value.relation.ordering)
}
}
private(set) var joins: OrderedDictionary<String, SQLQualifiedJoin>
let groupPromise: DatabasePromise<[SQLExpression]>?
let havingExpressionPromise: DatabasePromise<SQLExpression>?
let limit: SQLLimit?
let ctes: OrderedDictionary<String, SQLCTE>
init(_ relation: SQLRelation) {
// Qualify the source, so that it be disambiguated with an SQL alias
// if needed (when a select query uses the same table several times).
// This disambiguation job will be actually performed by
// SQLGenerationContext, when the SQLSelectQueryGenerator which owns
// this SQLQualifiedRelation generates SQL.
source = SQLQualifiedSource(relation.source)
// Qualify all selection, filter, etc, so that all identifiers
// can be correctly disambiguated and qualified.
let sourceAlias = source.alias
sourceSelectionPromise = relation.selectionPromise.map {
$0.map { $0.qualified(with: sourceAlias) }
}
filterPromise = relation.filterPromise.map {
$0.map { $0.qualified(with: sourceAlias) }
}
sourceOrdering = relation.ordering.qualified(with: sourceAlias)
groupPromise = relation.groupPromise?.map {
$0.map { $0.qualified(with: sourceAlias) }
}
havingExpressionPromise = relation.havingExpressionPromise.map {
$0.map { $0.qualified(with: sourceAlias) }
}
// Turns relation children into joins. `including(all:)` children are
// discarded on the way.
joins = relation.children.compactMapValues { SQLQualifiedJoin($0) }
// Copy other flags
limit = relation.limit
isDistinct = relation.isDistinct
ctes = relation.allCTEs
}
/// See SQLQueryGenerator.rowAdapter(_:)
///
/// - parameter startIndex: The index of the leftmost selected column of
/// this relation in a full SQL query.
/// - parameter rootRelation: True iff the relation is at the root of a
/// SQLQueryGenerator (as opposed to the joined relations).
/// - returns: An optional tuple made of a RowAdapter and the index past the
/// rightmost selected column of this relation. Nil is returned if this
/// relations does not need any row adapter.
func rowAdapter(
_ context: SQLGenerationContext,
fromIndex startIndex: Int,
rootRelation: Bool) throws
-> (adapter: RowAdapter, endIndex: Int)?
{
// Root relation && no join => no need for any adapter
if rootRelation && joins.isEmpty {
return nil
}
// The number of columns in source selection. Columns selected by joined
// relations are appended after.
let sourceSelectionWidth = try sourceSelectionPromise.resolve(context.db).columnCount(context)
// Recursively build adapters for each joined relation with a selection.
// Name them according to the join keys.
var endIndex = startIndex + sourceSelectionWidth
var scopes: [String: RowAdapter] = [:]
for (key, join) in joins {
if let (joinAdapter, joinEndIndex) = try join
.relation
.rowAdapter(context, fromIndex: endIndex, rootRelation: false)
{
scopes[key] = joinAdapter
endIndex = joinEndIndex
}
}
// (Root relation || empty selection) && no included relation => no need for any adapter
if (rootRelation || sourceSelectionWidth == 0) && scopes.isEmpty {
return nil
}
// Build a RangeRowAdapter extended with the adapters of joined relations.
//
// // SELECT book.*, author.* FROM book JOIN author ON author.id = book.authorId
// let request = Book.including(required: Book.author)
// for row in try Row.fetchAll(db, request) {
//
// The RangeRowAdapter hides the columns appended by joined relations:
//
// row // [id:1, title:"Moby-Dick"]
// let book = Book(row: row)
//
// Scopes give access to those joined relations:
//
// row.scopes["author"] // [id:12, name:"Herman Melville"]
// let author: Author = row["author"]
// }
let rangeAdapter = RangeRowAdapter(startIndex ..< (startIndex + sourceSelectionWidth))
let adapter = rangeAdapter.addingScopes(scopes)
return (adapter: adapter, endIndex: endIndex)
}
/// Sets the selection, removes all selections from joins, and clears the
/// `isDistinct` flag.
func selectOnly(_ selection: [SQLSelection]) -> Self {
let qualifiedSelection = selection.map {
$0.qualified(with: source.alias)
}
return with {
$0.sourceSelectionPromise = DatabasePromise(value: qualifiedSelection)
$0.isDistinct = false
$0.joins = $0.joins.mapValues { join in
join.with {
$0.relation = $0.relation.selectOnly([])
}
}
}
}
}
extension SQLQualifiedRelation: Refinable { }
/// A "qualified" source, where all tables are identified with a table alias.
private struct SQLQualifiedSource {
var tableName: String
var alias: TableAlias
init(_ source: SQLSource) {
self.tableName = source.tableName
self.alias = source.alias ?? TableAlias(tableName: source.tableName)
assert(alias.tableName == tableName)
}
func sql(_ context: SQLGenerationContext) throws -> String {
if let aliasName = context.aliasName(for: alias) {
return "\(tableName.quotedDatabaseIdentifier) \(aliasName.quotedDatabaseIdentifier)"
} else {
return "\(tableName.quotedDatabaseIdentifier)"
}
}
}
/// A "qualified" join, where all tables are identified with a table alias.
private struct SQLQualifiedJoin: Refinable {
enum Kind: String {
case leftJoin = "LEFT JOIN"
case innerJoin = "JOIN"
init?(_ kind: SQLRelation.Child.Kind) {
switch kind {
case .oneRequired:
self = .innerJoin
case .oneOptional:
self = .leftJoin
case .all, .bridge:
// Eager loading of to-many associations is not implemented with joins
return nil
}
}
}
var kind: Kind
var condition: SQLAssociationCondition
var relation: SQLQualifiedRelation
init?(_ child: SQLRelation.Child) {
guard let kind = Kind(child.kind) else {
return nil
}
self.kind = kind
self.condition = child.condition
self.relation = SQLQualifiedRelation(child.relation)
}
func sql(_ context: SQLGenerationContext, leftAlias: TableAlias) throws -> String {
try sql(context, leftAlias: leftAlias, allowingInnerJoin: true)
}
private func sql(
_ context: SQLGenerationContext,
leftAlias: TableAlias,
allowingInnerJoin allowsInnerJoin: Bool)
throws -> String
{
var allowsInnerJoin = allowsInnerJoin
switch self.kind {
case .innerJoin:
guard allowsInnerJoin else {
// TODO: chainOptionalRequired
//
// When we eventually implement this, make sure we both support:
// - joining(optional: assoc.joining(required: ...))
// - having(assoc.joining(required: ...).isEmpty)
fatalError("Not implemented: chaining a required association behind an optional association")
}
case .leftJoin:
allowsInnerJoin = false
}
// JOIN table...
var sql = try "\(kind.rawValue) \(relation.source.sql(context))"
// ... ON <join conditions> AND <other filters>
let rightAlias = relation.source.alias
var conditions: [SQLExpression] = []
if let expression = try condition.joinExpression(context.db,
leftAlias: leftAlias,
rightAlias: rightAlias)
{
conditions.append(expression)
}
if let filter = try relation.filterPromise?.resolve(context.db) {
conditions.append(filter.qualified(with: rightAlias))
}
if conditions.isEmpty == false {
sql += " ON "
sql += try conditions
.joined(operator: .and)
.sql(context)
}
for (_, join) in relation.joins {
// Right becomes left as we dig further
sql += try " \(join.sql(context, leftAlias: rightAlias, allowingInnerJoin: allowsInnerJoin))"
}
return sql
}
}