Generate update companions for data classes

moor/example/example.g.dart

@@ -59,6 +59,28 @@ class Category extends DataClass {
       (other is Category && other.id == id && other.description == description);
 }
 
+class CategoriesCompanion implements UpdateCompanion<Category> {
+  final Value<int> id;
+  final Value<String> description;
+  const CategoriesCompanion({
+    this.id = Value.absent(),
+    this.description = Value.absent(),
+  });
+  @override
+  bool isValuePresent(int index) {
+    switch (index) {
+      case 0:
+        return id.present;
+      case 1:
+        return description.present;
+      default:
+        throw ArgumentError(
+            'Hit an invalid state while serializing data. Did you run the build step?');
+    }
+    ;
+  }
+}
+
 class $CategoriesTable extends Categories
     with TableInfo<$CategoriesTable, Category> {
   final GeneratedDatabase _db;
@@ -203,6 +225,36 @@ class Recipe extends DataClass {
           other.category == category);
 }
 
+class RecipesCompanion implements UpdateCompanion<Recipe> {
+  final Value<int> id;
+  final Value<String> title;
+  final Value<String> instructions;
+  final Value<int> category;
+  const RecipesCompanion({
+    this.id = Value.absent(),
+    this.title = Value.absent(),
+    this.instructions = Value.absent(),
+    this.category = Value.absent(),
+  });
+  @override
+  bool isValuePresent(int index) {
+    switch (index) {
+      case 0:
+        return id.present;
+      case 1:
+        return title.present;
+      case 2:
+        return instructions.present;
+      case 3:
+        return category.present;
+      default:
+        throw ArgumentError(
+            'Hit an invalid state while serializing data. Did you run the build step?');
+    }
+    ;
+  }
+}
+
 class $RecipesTable extends Recipes with TableInfo<$RecipesTable, Recipe> {
   final GeneratedDatabase _db;
   final String _alias;
@@ -366,6 +418,32 @@ class Ingredient extends DataClass {
           other.caloriesPer100g == caloriesPer100g);
 }
 
+class IngredientsCompanion implements UpdateCompanion<Ingredient> {
+  final Value<int> id;
+  final Value<String> name;
+  final Value<int> caloriesPer100g;
+  const IngredientsCompanion({
+    this.id = Value.absent(),
+    this.name = Value.absent(),
+    this.caloriesPer100g = Value.absent(),
+  });
+  @override
+  bool isValuePresent(int index) {
+    switch (index) {
+      case 0:
+        return id.present;
+      case 1:
+        return name.present;
+      case 2:
+        return caloriesPer100g.present;
+      default:
+        throw ArgumentError(
+            'Hit an invalid state while serializing data. Did you run the build step?');
+    }
+    ;
+  }
+}
+
 class $IngredientsTable extends Ingredients
     with TableInfo<$IngredientsTable, Ingredient> {
   final GeneratedDatabase _db;
@@ -520,6 +598,33 @@ class IngredientInRecipe extends DataClass {
           other.amountInGrams == amountInGrams);
 }
 
+class IngredientInRecipesCompanion
+    implements UpdateCompanion<IngredientInRecipe> {
+  final Value<int> recipe;
+  final Value<int> ingredient;
+  final Value<int> amountInGrams;
+  const IngredientInRecipesCompanion({
+    this.recipe = Value.absent(),
+    this.ingredient = Value.absent(),
+    this.amountInGrams = Value.absent(),
+  });
+  @override
+  bool isValuePresent(int index) {
+    switch (index) {
+      case 0:
+        return recipe.present;
+      case 1:
+        return ingredient.present;
+      case 2:
+        return amountInGrams.present;
+      default:
+        throw ArgumentError(
+            'Hit an invalid state while serializing data. Did you run the build step?');
+    }
+    ;
+  }
+}
+
 class $IngredientInRecipesTable extends IngredientInRecipes
     with TableInfo<$IngredientInRecipesTable, IngredientInRecipe> {
   final GeneratedDatabase _db;

moor/lib/moor.dart

@@ -18,6 +18,7 @@ export 'package:moor/src/runtime/expressions/user_api.dart';
 export 'package:moor/src/runtime/executor/transactions.dart';
 export 'package:moor/src/runtime/statements/query.dart';
 export 'package:moor/src/runtime/statements/select.dart';
+export 'package:moor/src/runtime/statements/update.dart';
 export 'package:moor/src/runtime/statements/insert.dart';
 export 'package:moor/src/runtime/statements/delete.dart';
 export 'package:moor/src/runtime/structure/columns.dart';

moor/lib/src/runtime/data_class.dart

@@ -1,10 +1,11 @@
 import 'dart:convert';
 
 import 'package:meta/meta.dart';
+import 'package:moor/moor.dart';
 
 /// A common supertype for all data classes generated by moor. Data classes are
-/// immutable structures that represent a single row.
-abstract class DataClass {
+/// immutable structures that represent a single row in a database table.
+abstract class DataClass implements UpdateCompanion {
   const DataClass();
 
   /// Converts this object into a representation that can be encoded with
@@ -20,6 +21,9 @@ abstract class DataClass {
     return json.encode(toJson(serializer: serializer));
   }
 
+  @override
+  bool isValuePresent(int index) => true;
+
   /// Used internally be generated code
   @protected
   static dynamic parseJson(String jsonString) {
@@ -27,6 +31,31 @@ abstract class DataClass {
   }
 }
 
+/// An update companion for a [DataClass] which is used to write data into a
+/// database using [InsertStatement.insert] or [UpdateStatement.write].
+///
+/// See also:
+/// - https://github.com/simolus3/moor/issues/25
+abstract class UpdateCompanion<D extends DataClass> {
+  /// Used internally by moor.
+  ///
+  /// Returns true if the column at the position [index] has been explicitly
+  /// set to a value.
+  bool isValuePresent(int index);
+}
+
+/// A wrapper around arbitrary data [T] to indicate presence or absence
+/// explicitly.
+class Value<T> {
+  final bool present;
+  final T value;
+
+  const Value.use(this.value) : present = true;
+  const Value.absent()
+      : value = null,
+        present = false;
+}
+
 /// Serializer responsible for mapping atomic types from and to json.
 abstract class ValueSerializer {
   const ValueSerializer();

moor/lib/src/runtime/database.dart

@@ -88,7 +88,7 @@ mixin QueryEngine on DatabaseConnectionUser {
   /// to write data into the [table] by using [InsertStatement.insert].
   @protected
   @visibleForTesting
-  InsertStatement<T> into<T>(TableInfo<Table, T> table) =>
+  InsertStatement<T> into<T extends DataClass>(TableInfo<Table, T> table) =>
       InsertStatement<T>(this, table);
 
   /// Starts an [UpdateStatement] for the given table. You can use that

moor/lib/src/runtime/statements/insert.dart

@@ -6,11 +6,11 @@ import 'package:moor/src/runtime/components/component.dart';
 
 import 'update.dart';
 
-class InsertStatement<DataClass> {
+class InsertStatement<D extends DataClass> {
   @protected
   final QueryEngine database;
   @protected
-  final TableInfo<Table, DataClass> table;
+  final TableInfo<Table, D> table;
 
   InsertStatement(this.database, this.table);
 
@@ -26,7 +26,7 @@ class InsertStatement<DataClass> {
   ///
   /// If the table contains an auto-increment column, the generated value will
   /// be returned.
-  Future<int> insert(DataClass entity, {bool orReplace = false}) async {
+  Future<int> insert(D entity, {bool orReplace = false}) async {
     _validateIntegrity(entity);
     final ctx = _createContext(entity, orReplace);
 
@@ -45,7 +45,7 @@ class InsertStatement<DataClass> {
   /// When a row with the same primary or unique key already exists in the
   /// database, the insert will fail. Use [orReplace] to replace rows that
   /// already exist.
-  Future<void> insertAll(List<DataClass> rows, {bool orReplace = false}) async {
+  Future<void> insertAll(List<D> rows, {bool orReplace = false}) async {
     final statements = <String, List<GenerationContext>>{};
 
     // Not every insert has the same sql, as fields which are set to null are
@@ -78,11 +78,11 @@ class InsertStatement<DataClass> {
   ///
   /// However, if no such row exists, a new row will be written instead.
   @Deprecated('Use insert with orReplace: true instead')
-  Future<void> insertOrReplace(DataClass entity) async {
+  Future<void> insertOrReplace(D entity) async {
     return await insert(entity, orReplace: true);
   }
 
-  GenerationContext _createContext(DataClass entry, bool replace) {
+  GenerationContext _createContext(D entry, bool replace) {
     final map = table.entityToSql(entry)
       ..removeWhere((_, value) => value == null);
 
@@ -111,7 +111,7 @@ class InsertStatement<DataClass> {
     return ctx;
   }
 
-  void _validateIntegrity(DataClass d) {
+  void _validateIntegrity(D d) {
     if (d == null) {
       throw InvalidDataException(
           'Cannot writee null row into ${table.$tableName}');

moor/test/data/tables/todos.g.dart

@@ -97,6 +97,40 @@ class TodoEntry extends DataClass {
           other.category == category);
 }
 
+class TodosTableCompanion implements UpdateCompanion<TodoEntry> {
+  final Value<int> id;
+  final Value<String> title;
+  final Value<String> content;
+  final Value<DateTime> targetDate;
+  final Value<int> category;
+  const TodosTableCompanion({
+    this.id = Value.absent(),
+    this.title = Value.absent(),
+    this.content = Value.absent(),
+    this.targetDate = Value.absent(),
+    this.category = Value.absent(),
+  });
+  @override
+  bool isValuePresent(int index) {
+    switch (index) {
+      case 0:
+        return id.present;
+      case 1:
+        return title.present;
+      case 2:
+        return content.present;
+      case 3:
+        return targetDate.present;
+      case 4:
+        return category.present;
+      default:
+        throw ArgumentError(
+            'Hit an invalid state while serializing data. Did you run the build step?');
+    }
+    ;
+  }
+}
+
 class $TodosTableTable extends TodosTable
     with TableInfo<$TodosTableTable, TodoEntry> {
   final GeneratedDatabase _db;
@@ -271,6 +305,28 @@ class Category extends DataClass {
       (other is Category && other.id == id && other.description == description);
 }
 
+class CategoriesCompanion implements UpdateCompanion<Category> {
+  final Value<int> id;
+  final Value<String> description;
+  const CategoriesCompanion({
+    this.id = Value.absent(),
+    this.description = Value.absent(),
+  });
+  @override
+  bool isValuePresent(int index) {
+    switch (index) {
+      case 0:
+        return id.present;
+      case 1:
+        return description.present;
+      default:
+        throw ArgumentError(
+            'Hit an invalid state while serializing data. Did you run the build step?');
+    }
+    ;
+  }
+}
+
 class $CategoriesTable extends Categories
     with TableInfo<$CategoriesTable, Category> {
   final GeneratedDatabase _db;
@@ -434,6 +490,40 @@ class User extends DataClass {
           other.creationTime == creationTime);
 }
 
+class UsersCompanion implements UpdateCompanion<User> {
+  final Value<int> id;
+  final Value<String> name;
+  final Value<bool> isAwesome;
+  final Value<Uint8List> profilePicture;
+  final Value<DateTime> creationTime;
+  const UsersCompanion({
+    this.id = Value.absent(),
+    this.name = Value.absent(),
+    this.isAwesome = Value.absent(),
+    this.profilePicture = Value.absent(),
+    this.creationTime = Value.absent(),
+  });
+  @override
+  bool isValuePresent(int index) {
+    switch (index) {
+      case 0:
+        return id.present;
+      case 1:
+        return name.present;
+      case 2:
+        return isAwesome.present;
+      case 3:
+        return profilePicture.present;
+      case 4:
+        return creationTime.present;
+      default:
+        throw ArgumentError(
+            'Hit an invalid state while serializing data. Did you run the build step?');
+    }
+    ;
+  }
+}
+
 class $UsersTable extends Users with TableInfo<$UsersTable, User> {
   final GeneratedDatabase _db;
   final String _alias;
@@ -602,6 +692,28 @@ class SharedTodo extends DataClass {
       (other is SharedTodo && other.todo == todo && other.user == user);
 }
 
+class SharedTodosCompanion implements UpdateCompanion<SharedTodo> {
+  final Value<int> todo;
+  final Value<int> user;
+  const SharedTodosCompanion({
+    this.todo = Value.absent(),
+    this.user = Value.absent(),
+  });
+  @override
+  bool isValuePresent(int index) {
+    switch (index) {
+      case 0:
+        return todo.present;
+      case 1:
+        return user.present;
+      default:
+        throw ArgumentError(
+            'Hit an invalid state while serializing data. Did you run the build step?');
+    }
+    ;
+  }
+}
+
 class $SharedTodosTable extends SharedTodos
     with TableInfo<$SharedTodosTable, SharedTodo> {
   final GeneratedDatabase _db;
@@ -731,6 +843,28 @@ class TableWithoutPKData extends DataClass {
           other.someFloat == someFloat);
 }
 
+class TableWithoutPKCompanion implements UpdateCompanion<TableWithoutPKData> {
+  final Value<int> notReallyAnId;
+  final Value<double> someFloat;
+  const TableWithoutPKCompanion({
+    this.notReallyAnId = Value.absent(),
+    this.someFloat = Value.absent(),
+  });
+  @override
+  bool isValuePresent(int index) {
+    switch (index) {
+      case 0:
+        return notReallyAnId.present;
+      case 1:
+        return someFloat.present;
+      default:
+        throw ArgumentError(
+            'Hit an invalid state while serializing data. Did you run the build step?');
+    }
+    ;
+  }
+}
+
 class $TableWithoutPKTable extends TableWithoutPK
     with TableInfo<$TableWithoutPKTable, TableWithoutPKData> {
   final GeneratedDatabase _db;

moor_generator/lib/src/model/specified_table.dart

@@ -10,6 +10,7 @@ class SpecifiedTable {
   final String dartTypeName;
 
   String get tableInfoName => tableInfoNameForTableClass(fromClass);
+  String get updateCompanionName => _updateCompanionName(fromClass);
 
   /// The set of primary keys, if they have been explicitly defined by
   /// overriding `primaryKey` in the table class. `null` if the primary key has
@@ -26,3 +27,6 @@ class SpecifiedTable {
 
 String tableInfoNameForTableClass(ClassElement fromClass) =>
     '\$${fromClass.name}Table';
+
+String _updateCompanionName(ClassElement fromClass) =>
+    '${fromClass.name}Companion';

moor_generator/lib/src/writer/table_writer.dart

@@ -2,6 +2,7 @@ import 'package:moor_generator/src/model/specified_column.dart';
 import 'package:moor_generator/src/model/specified_table.dart';
 import 'package:moor_generator/src/options.dart';
 import 'package:moor_generator/src/writer/data_class_writer.dart';
+import 'package:moor_generator/src/writer/update_companion_writer.dart';
 import 'package:moor_generator/src/writer/utils.dart';
 
 class TableWriter {
@@ -17,6 +18,7 @@ class TableWriter {
 
   void writeDataClass(StringBuffer buffer) {
     DataClassWriter(table, options).writeInto(buffer);
+    UpdateCompanionWriter(table, options).writeInto(buffer);
   }
 
   void writeTableInfoClass(StringBuffer buffer) {

moor_generator/lib/src/writer/update_companion_writer.dart

@@ -0,0 +1,53 @@
+import 'package:moor_generator/src/model/specified_table.dart';
+import 'package:moor_generator/src/options.dart';
+
+class UpdateCompanionWriter {
+  final SpecifiedTable table;
+  final MoorOptions options;
+
+  UpdateCompanionWriter(this.table, this.options);
+
+  void writeInto(StringBuffer buffer) {
+    buffer.write('class ${table.updateCompanionName} '
+        'implements UpdateCompanion<${table.dartTypeName}> {\n');
+    _writeFields(buffer);
+    _writeConstructor(buffer);
+    _writeIsPresentOverride(buffer);
+
+    buffer.write('}\n');
+  }
+
+  void _writeFields(StringBuffer buffer) {
+    for (var column in table.columns) {
+      buffer.write('final Value<${column.dartTypeName}>'
+          ' ${column.dartGetterName};\n');
+    }
+  }
+
+  void _writeConstructor(StringBuffer buffer) {
+    buffer.write('const ${table.updateCompanionName}({');
+
+    for (var column in table.columns) {
+      buffer.write('this.${column.dartGetterName} = Value.absent(),');
+    }
+
+    buffer.write('});\n');
+  }
+
+  void _writeIsPresentOverride(StringBuffer buffer) {
+    buffer
+      ..write('@override\nbool isValuePresent(int index) {\n')
+      ..write('switch (index) {');
+
+    for (var i = 0; i < table.columns.length; i++) {
+      final getterName = table.columns[i].dartGetterName;
+      buffer.write('case $i: return $getterName.present;\n');
+    }
+
+    buffer
+      ..write('default: throw ArgumentError('
+          "'Hit an invalid state while serializing data. Did you run the build "
+          "step?');")
+      ..write('};}\n');
+  }
+}