Use DROP/RENAME COLUMN when available

Author: jberkel

Sources/SQLite/Schema/Connection+Schema.swift

@@ -1,6 +1,19 @@
 import Foundation
 
 extension Connection {
+    var sqliteVersion: String? {
+        (try? scalar("SELECT sqlite_version()")) as? String
+    }
+
+    var sqliteVersionTriple: (Int, Int, Int) {
+        guard let version = sqliteVersion,
+              let splits = .some(version.split(separator: ".", maxSplits: 3)), splits.count == 3,
+              let major = Int(splits[0]), let minor = Int(splits[1]), let point = Int(splits[2]) else {
+            return (0, 0, 0)
+        }
+        return (major, minor, point)
+    }
+
     // Changing the foreign_keys setting affects the execution of all statements prepared using the database
     // connection, including those prepared before the setting was changed.
     //

Sources/SQLite/Schema/SchemaChanger.swift

@@ -27,6 +27,8 @@ import Foundation
        12. If foreign keys constraints were originally enabled, reenable them now.
 */
 public class SchemaChanger: CustomStringConvertible {
+    typealias SQLiteVersion = (Int, Int, Int)
+
     enum SchemaChangeError: LocalizedError {
         case foreignKeyError([ForeignKeyError])
 
@@ -46,9 +48,14 @@ public class SchemaChanger: CustomStringConvertible {
         case renameTable(String)
 
         /// Returns non-nil if the operation can be executed with a simple SQL statement
-        func toSQL(_ table: String) -> String? {
+        func toSQL(_ table: String, version: SQLiteVersion) -> String? {
             switch self {
-            case .add(let definition): return "ALTER TABLE \(table.quote()) ADD COLUMN \(definition.toSQL())"
+            case .add(let definition):
+                return "ALTER TABLE \(table.quote()) ADD COLUMN \(definition.toSQL())"
+            case .renameColumn(let from, let to) where version.0 >= 3 && version.1 >= 25:
+                return "ALTER TABLE \(table.quote()) RENAME COLUMN \(from.quote()) TO \(to.quote())"
+            case .remove(let column) where version.0 >= 3 && version.1 >= 35:
+                return "ALTER TABLE \(table.quote()) DROP COLUMN \(column.quote())"
             default: return nil
             }
         }
@@ -77,6 +84,7 @@ public class SchemaChanger: CustomStringConvertible {
     }
 
     private let connection: Connection
+    private let version: SQLiteVersion
     static let tempPrefix = "tmp_"
     typealias Block = () throws -> Void
     public typealias AlterTableDefinitionBlock = (AlterTableDefinition) -> Void
@@ -87,8 +95,14 @@ public class SchemaChanger: CustomStringConvertible {
         static let temp = Options(rawValue: 1)
     }
 
-    public init(connection: Connection) {
+    public convenience init(connection: Connection) {
+        self.init(connection: connection,
+                  version: connection.sqliteVersionTriple)
+    }
+
+    init(connection: Connection, version: SQLiteVersion) {
         self.connection = connection
+        self.version = version
     }
 
     public func alter(table: String, block: AlterTableDefinitionBlock) throws {
@@ -105,7 +119,7 @@ public class SchemaChanger: CustomStringConvertible {
     }
 
     private func run(table: String, operation: Operation) throws {
-        if let sql = operation.toSQL(table) {
+        if let sql = operation.toSQL(table, version: version) {
             try connection.run(sql)
         } else {
             try doTheTableDance(table: table, operation: operation)

Tests/SQLiteTests/Schema/ConnectionSchemaTests.swift

@@ -136,4 +136,11 @@ class ConnectionSchemaTests: SQLiteTestCase {
             ForeignKeyDefinition(table: "users", column: "test_id", primaryKey: "id", onUpdate: nil, onDelete: nil)
         ])
     }
+
+    func test_sqlite_version_triple() {
+        let version = db.sqliteVersionTriple
+        XCTAssertEqual(version.0, 3)
+        XCTAssertGreaterThan(version.1, 0)
+        XCTAssertGreaterThanOrEqual(version.2, 0)
+    }
 }

Tests/SQLiteTests/Schema/SchemaChangerTests.swift

@@ -57,6 +57,16 @@ class SchemaChangerTests: SQLiteTestCase {
         XCTAssertFalse(columns.contains("age"))
     }
 
+    func test_remove_column_legacy() throws {
+        schemaChanger = .init(connection: db, version: (3, 24, 0)) // DROP COLUMN introduced in 3.35.0
+
+        try schemaChanger.alter(table: "users") { table in
+            table.remove("age")
+        }
+        let columns = try db.columnInfo(table: "users").map(\.name)
+        XCTAssertFalse(columns.contains("age"))
+    }
+
     func test_rename_column() throws {
         try schemaChanger.alter(table: "users") { table in
             table.rename("age", to: "age2")
@@ -67,6 +77,18 @@ class SchemaChangerTests: SQLiteTestCase {
         XCTAssertTrue(columns.contains("age2"))
     }
 
+    func test_rename_column_legacy() throws {
+        schemaChanger = .init(connection: db, version: (3, 24, 0)) // RENAME COLUMN introduced in 3.25.0
+
+        try schemaChanger.alter(table: "users") { table in
+            table.rename("age", to: "age2")
+        }
+
+        let columns = try db.columnInfo(table: "users").map(\.name)
+        XCTAssertFalse(columns.contains("age"))
+        XCTAssertTrue(columns.contains("age2"))
+    }
+
     func test_add_column() throws {
         let newColumn = ColumnDefinition(name: "new_column", primaryKey: nil, type: .TEXT, null: true, defaultValue: .NULL, references: nil)
 

Tests/SQLiteTests/Schema/SchemaDefinitionsTests.swift

@@ -29,6 +29,7 @@ class ColumnDefinitionTests: XCTestCase {
         "\"real_column\" REAL DEFAULT 123.123")
     ]
 
+    #if !os(Linux)
     override class var defaultTestSuite: XCTestSuite {
         let suite = XCTestSuite(forTestCaseClass: ColumnDefinitionTests.self)
 
@@ -44,6 +45,7 @@ class ColumnDefinitionTests: XCTestCase {
     @objc func verify() {
         XCTAssertEqual(definition.toSQL(), expected)
     }
+    #endif
 }
 
 class AffinityTests: XCTestCase {
@@ -105,6 +107,7 @@ class IndexDefinitionTests: XCTestCase {
         "CREATE INDEX IF NOT EXISTS \"index_tests\" ON \"tests\" (\"test_column\")")
     ]
 
+    #if !os(Linux)
     override class var defaultTestSuite: XCTestSuite {
         let suite = XCTestSuite(forTestCaseClass: IndexDefinitionTests.self)
 
@@ -121,6 +124,7 @@ class IndexDefinitionTests: XCTestCase {
     @objc func verify() {
         XCTAssertEqual(definition.toSQL(ifNotExists: ifNotExists), expected)
     }
+    #endif
 
     func test_validate() {