Support mapping BLOBs to literals

moor/CHANGELOG.md

@@ -53,7 +53,7 @@ TODO: Describe ffi port
 
 ### Minor changes
 - a `Constant<String>` can now be written to SQL, it used to throw before. This is useful
-  if you need default values for strings columns.
+  if you need default values for strings columns. This also works for `BLOBS`.
 - new `LazyDatabase` when you want to construct a database asynchronously (for instance, if
   you first need to find a file before you can open a database).
 

moor/lib/src/types/sql_types.dart

@@ -1,5 +1,7 @@
 import 'dart:typed_data';
 
+import 'package:convert/convert.dart';
+
 part 'custom_type.dart';
 
 /// A type that can be mapped from Dart to sql. The generic type parameter here
@@ -118,12 +120,14 @@ class BlobType extends SqlType<Uint8List> {
   mapFromDatabaseResponse(response) => response as Uint8List;
 
   @override
-  String mapToSqlConstant(content) {
-    throw UnimplementedError("Blobs can't be mapped to sql literals");
+  String mapToSqlConstant(Uint8List content) {
+    // BLOB literals are string literals containing hexadecimal data and
+    // preceded by a single "x" or "X" character. Example: X'53514C697465'
+    return "x'${hex.encode(content)}'";
   }
 
   @override
-  mapToSqlVariable(content) => content;
+  mapToSqlVariable(Uint8List content) => content;
 }
 
 class RealType extends SqlType<double> {

moor/pubspec.yaml

@@ -13,6 +13,7 @@ environment:
 
 dependencies:
   meta: ^1.0.0
+  convert: ^2.1.1
   collection: ^1.0.0
   synchronized: ^2.1.0
   pedantic: ^1.0.0

moor/test/types/blob_test.dart

@@ -0,0 +1,22 @@
+import 'dart:convert';
+
+import 'package:moor/moor.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test('maps without transormation', () {
+    const type = BlobType();
+    final data = Uint8List.fromList(List.generate(256, (i) => i));
+
+    expect(type.mapToSqlVariable(data), data);
+    expect(type.mapFromDatabaseResponse(data), data);
+  });
+
+  test('writes blob literals', () {
+    const type = BlobType();
+    const hex = '67656E6572616C206B656E6F626921';
+    final data = Uint8List.fromList(utf8.encode('general kenobi!'));
+
+    expect(type.mapToSqlConstant(data), equalsIgnoringCase("x'$hex'"));
+  });
+}