Add columns via Expressions

Author: jberkel

Sources/SQLite/Schema/SchemaChanger.swift

@@ -136,6 +136,14 @@ public class SchemaChanger: CustomStringConvertible {
             columnDefinitions.append(column)
         }
 
+        public func add<T>(expression: Expression<T>) where T: Value {
+            add(column: .init(name: columnName(for: expression), type: .init(expression: expression), nullable: false))
+        }
+
+        public func add<T>(expression: Expression<T?>) where T: Value {
+            add(column: .init(name: columnName(for: expression), type: .init(expression: expression), nullable: true))
+        }
+
         public func add(index: IndexDefinition) {
             indexDefinitions.append(index)
         }
@@ -146,6 +154,13 @@ public class SchemaChanger: CustomStringConvertible {
                 .createTable(columns: columnDefinitions, ifNotExists: ifNotExists)
             ] + indexDefinitions.map { .addIndex($0) }
         }
+
+        private func columnName<T>(for expression: Expression<T>) -> String {
+            switch LiteralValue(expression.template) {
+            case .stringLiteral(let string): return string
+            default: fatalError("expression is not a literal string value")
+            }
+        }
     }
 
     private let connection: Connection
@@ -331,3 +346,13 @@ extension TableDefinition {
         }
     }
 }
+
+extension ColumnDefinition.Affinity {
+    init<T>(expression: Expression<T>) where T: Value {
+        self.init(T.declaredDatatype)
+    }
+
+    init<T>(expression: Expression<T?>) where T: Value {
+        self.init(T.declaredDatatype)
+    }
+}

Tests/SQLiteTests/Schema/SchemaChangerTests.swift

@@ -201,6 +201,36 @@ class SchemaChangerTests: SQLiteTestCase {
         ])
     }
 
+    func test_create_table_add_column_expression() throws {
+        try schemaChanger.create(table: "foo") { table in
+            table.add(expression: Expression<String>("name"))
+            table.add(expression: Expression<Int>("age"))
+            table.add(expression: Expression<Double?>("salary"))
+        }
+
+        let columns = try schema.columnDefinitions(table: "foo")
+        XCTAssertEqual(columns, [
+            ColumnDefinition(name: "name",
+                             primaryKey: nil,
+                             type: .TEXT,
+                             nullable: false,
+                             defaultValue: .NULL,
+                             references: nil),
+            ColumnDefinition(name: "age",
+                             primaryKey: nil,
+                             type: .INTEGER,
+                             nullable: false,
+                             defaultValue: .NULL,
+                             references: nil),
+            ColumnDefinition(name: "salary",
+                             primaryKey: nil,
+                             type: .REAL,
+                             nullable: true,
+                             defaultValue: .NULL,
+                             references: nil)
+            ])
+    }
+
     func test_create_table_if_not_exists() throws {
         try schemaChanger.create(table: "foo") { table in
             table.add(column: .init(name: "id", primaryKey: .init(autoIncrement: true), type: .INTEGER))