Support INSTEAD OF triggers

After adding support for database views (#172) it is easy enough to
support triggers for them, so let's do so!

Author: stephencelis

Sources/StructuredQueriesSQLiteCore/Documentation.docc/Articles/Triggers.md

@@ -188,6 +188,7 @@ reminder is inserted into the database with the  following trigger:
 
 - ``StructuredQueriesCore/Table/createTemporaryTrigger(_:ifNotExists:after:fileID:line:column:)``
 - ``StructuredQueriesCore/Table/createTemporaryTrigger(_:ifNotExists:before:fileID:line:column:)``
+- ``StructuredQueriesCore/Table/createTemporaryTrigger(_:ifNotExists:insteadOf:fileID:line:column:)``
 
 ### Touching records
 

Sources/StructuredQueriesSQLiteCore/Triggers.swift

@@ -74,6 +74,42 @@ extension Table {
     )
   }
 
+  /// A `CREATE TEMPORARY TRIGGER` statement that executes instead of a database view event.
+  ///
+  /// See <doc:Triggers> for more information.
+  ///
+  /// > Important: A name for the trigger is automatically derived from the arguments if one is not
+  /// > provided. If you build your own trigger helper that call this function, then your helper
+  /// > should also take `fileID`, `line` and `column` arguments and pass them to this function.
+  ///
+  /// - Parameters:
+  ///   - name: The trigger's name. By default a unique name is generated depending using the table,
+  ///     operation, and source location.
+  ///   - ifNotExists: Adds an `IF NOT EXISTS` clause to the `CREATE TRIGGER` statement.
+  ///   - operation: The trigger's operation.
+  ///   - fileID: The source `#fileID` associated with the trigger.
+  ///   - line: The source `#line` associated with the trigger.
+  ///   - column: The source `#column` associated with the trigger.
+  /// - Returns: A temporary trigger.
+  public static func createTemporaryTrigger(
+    _ name: String? = nil,
+    ifNotExists: Bool = false,
+    insteadOf operation: TemporaryTrigger<Self>.Operation,
+    fileID: StaticString = #fileID,
+    line: UInt = #line,
+    column: UInt = #column
+  ) -> TemporaryTrigger<Self> {
+    TemporaryTrigger(
+      name: name,
+      ifNotExists: ifNotExists,
+      operation: operation,
+      when: .insteadOf,
+      fileID: fileID,
+      line: line,
+      column: column
+    )
+  }
+
   /// A `CREATE TEMPORARY TRIGGER` statement that applies additional updates to a row that has just
   /// been updated.
   ///
@@ -252,6 +288,7 @@ public struct TemporaryTrigger<On: Table>: Sendable, Statement {
   fileprivate enum When: QueryFragment {
     case before = "BEFORE"
     case after = "AFTER"
+    case insteadOf = "INSTEAD OF"
   }
 
   /// The database event used in a trigger.

Tests/StructuredQueriesTests/ViewsTests.swift

@@ -54,6 +54,62 @@ extension SnapshotTests {
         └────────────────────────┘
         """
       }
+      assertQuery(
+        CompletedReminder.createTemporaryTrigger(
+          insteadOf: .insert { new in
+            Reminder.insert {
+              ($0.id, $0.title, $0.isCompleted, $0.remindersListID)
+            } values: {
+              (Reminder.select { ($0.id.max() ?? 0) + 1 }, new.title, true, 1)
+            }
+          }
+        )
+      ) {
+        """
+        CREATE TEMPORARY TRIGGER
+          "after_insert_on_completedReminders@StructuredQueriesTests/ViewsTests.swift:58:49"
+        INSTEAD OF INSERT ON "completedReminders"
+        FOR EACH ROW BEGIN
+          INSERT INTO "reminders"
+          ("id", "title", "isCompleted", "remindersListID")
+          VALUES
+          ((
+            SELECT (coalesce(max("reminders"."id"), 0) + 1)
+            FROM "reminders"
+          ), "new"."title", 1, 1);
+        END
+        """
+      }
+      assertQuery(
+        CompletedReminder.insert(\.title) { "Already done" }
+      ) {
+        """
+        INSERT INTO "completedReminders"
+        ("title")
+        VALUES
+        ('Already done')
+        """
+      }
+      // NB: Can't use 'RETURNING' above due to a SQLite bug where 'reminderID' is 'NULL'.
+      assertQuery(
+        CompletedReminder.order { $0.reminderID.desc() }.limit(1)
+      ) {
+        """
+        SELECT "completedReminders"."reminderID", "completedReminders"."title"
+        FROM "completedReminders"
+        ORDER BY "completedReminders"."reminderID" DESC
+        LIMIT 1
+        """
+      } results: {
+        """
+        ┌─────────────────────────┐
+        │ CompletedReminder(      │
+        │   reminderID: 11,       │
+        │   title: "Already done" │
+        │ )                       │
+        └─────────────────────────┘
+        """
+      }
       assertQuery(
         query.drop()
       ) {