Define API for default values

moor/lib/src/dsl/columns.dart

@@ -32,7 +32,11 @@ abstract class BlobColumn extends Column<Uint8List, BlobType> {}
 /// be called at runtime. Instead, moor_generator will take a look at your
 /// source code (specifically, it will analyze which of the methods you use) to
 /// figure out the column structure of a table.
-class ColumnBuilder<Builder, ResultColumn> {
+class ColumnBuilder<
+    Builder,
+    ResultColumn extends Column<ResultDartType, ResultSqlType>,
+    ResultSqlType extends SqlType<ResultDartType>,
+    ResultDartType> {
   /// By default, the field name will be used as the column name, e.g.
   /// `IntColumn get id = integer()` will have "id" as its associated name.
   /// Columns made up of multiple words are expected to be in camelCase and will
@@ -53,7 +57,7 @@ class ColumnBuilder<Builder, ResultColumn> {
   /// `name TYPE NULLABILITY NATIVE_CONSTRAINTS`. Native constraints are used to
   /// enforce that booleans are either 0 or 1 (e.g.
   /// `field BOOLEAN NOT NULL CHECK (field in (0, 1)`). Auto-Increment
-  /// columns also make use of the native constraints.
+  /// columns also make use of the native constraints, as do default values.
   /// If [customConstraint] has been called, the nullability information and
   /// native constraints will never be written. Instead, they will be replaced
   /// with the [constraint]. For example, if you call
@@ -73,23 +77,36 @@ class ColumnBuilder<Builder, ResultColumn> {
   /// - [GeneratedColumn.writeCustomConstraints]
   Builder customConstraint(String constraint) => null;
 
+  /// The column will use this expression when a row is inserted and no value
+  /// has been specified.
+  ///
+  /// See also:
+  /// - [Constant], which can be used to model literals that appear in CREATE
+  /// TABLE statements.
+  /// - [currentDate] and [currentDateAndTime], which are useful expressions to
+  /// store the current date/time as a default value.
+  Builder withDefault(Expression<ResultDartType, ResultSqlType> e) => null;
+
   /// Turns this column builder into a column. This method won't actually be
   /// called in your code. Instead, moor_generator will take a look at your
   /// source code to figure out your table structure.
   ResultColumn call() => null;
 }
 
-class IntColumnBuilder extends ColumnBuilder<IntColumnBuilder, IntColumn> {
+class IntColumnBuilder extends ColumnBuilder<IntColumnBuilder, IntColumn, IntType, int> {
   /// Enables auto-increment for this column, which will also make this column
   /// the primary key of the table.
   IntColumnBuilder autoIncrement() => this;
 }
 
-class BoolColumnBuilder extends ColumnBuilder<BoolColumnBuilder, BoolColumn> {}
+class BoolColumnBuilder
+    extends ColumnBuilder<BoolColumnBuilder, BoolColumn, BoolType, bool> {}
 
-class BlobColumnBuilder extends ColumnBuilder<BlobColumnBuilder, BlobColumn> {}
+class BlobColumnBuilder
+    extends ColumnBuilder<BlobColumnBuilder, BlobColumn, BlobType, Uint8List> {}
 
-class TextColumnBuilder extends ColumnBuilder<TextColumnBuilder, TextColumn> {
+class TextColumnBuilder
+    extends ColumnBuilder<TextColumnBuilder, TextColumn, StringType, String> {
   /// Puts a constraint on the minimum and maximum length of text that can be
   /// stored in this column (will be validated whenever this column is updated
   /// or a value is inserted). If [min] is not null and one tries to write a
@@ -100,4 +117,4 @@ class TextColumnBuilder extends ColumnBuilder<TextColumnBuilder, TextColumn> {
 }
 
 class DateTimeColumnBuilder
-    extends ColumnBuilder<DateTimeColumnBuilder, DateTimeColumn> {}
+    extends ColumnBuilder<DateTimeColumnBuilder, DateTimeColumn, DateTimeType, DateTime> {}

moor/lib/src/runtime/expressions/custom.dart

@@ -5,7 +5,7 @@ import 'package:moor/src/runtime/expressions/expression.dart';
 class CustomExpression<D, S extends SqlType<D>> extends Expression<D, S> {
   final String content;
 
-  CustomExpression(this.content);
+  const CustomExpression(this.content);
 
   @override
   void writeInto(GenerationContext context) {

moor/lib/src/runtime/expressions/datetimes.dart

@@ -1,5 +1,6 @@
 import 'package:moor/moor.dart';
 import 'package:moor/src/runtime/components/component.dart';
+import 'package:moor/src/runtime/expressions/custom.dart';
 import 'package:moor/src/runtime/expressions/expression.dart';
 
 /// Extracts the (UTC) year from the given expression that resolves
@@ -32,6 +33,15 @@ Expression<int, IntType> minute(Expression<DateTime, DateTimeType> date) =>
 Expression<int, IntType> second(Expression<DateTime, DateTimeType> date) =>
     _StrftimeSingleFieldExpression('%S', date);
 
+/// A sql expression that evaluates to the current date represented as a unix
+/// timestamp. The hour, minute and second fields will be set to 0.
+const Expression<DateTime, DateTimeType> currentDate =
+    CustomExpression("strftime('%s', CURRENT_DATE)");
+/// A sql expression that evaluates to the current date and time, similar to
+/// [DateTime.now]. Timestamps are stored with a second accuracy.
+const Expression<DateTime, DateTimeType> currentDateAndTime =
+    CustomExpression("strftime('%s', CURRENT_TIMESTAMP)");
+
 /// Expression that extracts components out of a date time by using the builtin
 /// sqlite function "strftime" and casting the result to an integer.
 class _StrftimeSingleFieldExpression extends Expression<int, IntType> {

moor/lib/src/runtime/expressions/expression.dart

@@ -7,6 +7,10 @@ import 'package:moor/src/types/sql_types.dart';
 /// include queries (which might evaluate to multiple values) but individual
 /// columns, functions and operators.
 abstract class Expression<D, T extends SqlType<D>> implements Component {
+  const Expression();
+
+  bool get isLiteral => false;
+
   /// Whether this expression is equal to the given expression.
   Expression<bool, BoolType> equalsExp(Expression<D, T> compare) =>
       Comparison.equal(this, compare);
@@ -21,7 +25,7 @@ abstract class Expression<D, T extends SqlType<D>> implements Component {
 
 /// An expression that looks like "$a operator $b", where $a and $b itself
 /// are expressions and the operator is any string.
-abstract class InfixOperator<D, T extends SqlType<D>> with Expression<D, T> {
+abstract class InfixOperator<D, T extends SqlType<D>> extends Expression<D, T> {
   Expression get left;
   Expression get right;
   String get operator;

moor/lib/src/runtime/expressions/variables.dart

@@ -9,7 +9,7 @@ import 'package:moor/src/types/sql_types.dart';
 class Variable<T, S extends SqlType<T>> extends Expression<T, S> {
   final T value;
 
-  Variable(this.value);
+  const Variable(this.value);
 
   /// Creates a variable that holds the specified boolean.
   static Variable<bool, BoolType> withBool(bool value) {
@@ -60,9 +60,12 @@ class Variable<T, S extends SqlType<T>> extends Expression<T, S> {
 /// yet as it can be vulnerable to SQL-injection attacks. Please use [Variable]
 /// instead.
 class Constant<T, S extends SqlType<T>> extends Expression<T, S> {
+  const Constant(this.value);
+
   final T value;
 
-  Constant(this.value);
+  @override
+  final bool isLiteral = true;
 
   @override
   void writeInto(GenerationContext context) {

moor/lib/src/runtime/structure/columns.dart

@@ -13,7 +13,6 @@ import 'package:moor/sqlite_keywords.dart';
 abstract class GeneratedColumn<T, S extends SqlType<T>> extends Column<T, S> {
   /// The sql name of this column.
   final String $name;
-
   String get escapedName => escapeIfNeeded($name);
 
   /// The name of the table that contains this column
@@ -27,8 +26,12 @@ abstract class GeneratedColumn<T, S extends SqlType<T>> extends Column<T, S> {
   /// field is going to be null.
   final String $customConstraints;
 
+  /// The default expression to be used during inserts when no value has been
+  /// specified. Can be null if no default value is set.
+  final Expression<T, S> defaultValue;
+
   GeneratedColumn(this.$name, this.tableName, this.$nullable,
-      {this.$customConstraints});
+      {this.$customConstraints, this.defaultValue});
 
   /// Writes the definition of this column, as defined
   /// [here](https://www.sqlite.org/syntax/column-def.html), into the given
@@ -68,8 +71,10 @@ abstract class GeneratedColumn<T, S extends SqlType<T>> extends Column<T, S> {
   /// method should check whether the value is valid for an update. Null values
   /// should always be accepted for updates, as the describe a value that should
   /// not be replaced.
-  bool isAcceptableValue(T value, bool duringInsert) =>
-      ($nullable || !duringInsert) || value != null;
+  bool isAcceptableValue(T value, bool duringInsert) {
+    final nullOk = !duringInsert || $nullable || defaultValue != null;
+    return nullOk || value != null;
+  }
 }
 
 class GeneratedTextColumn extends GeneratedColumn<String, StringType>
@@ -77,10 +82,16 @@ class GeneratedTextColumn extends GeneratedColumn<String, StringType>
   final int minTextLength;
   final int maxTextLength;
 
-  GeneratedTextColumn(String name, String tableName, bool nullable,
-      {this.minTextLength, this.maxTextLength, String $customConstraints})
-      : super(name, tableName, nullable,
-            $customConstraints: $customConstraints);
+  GeneratedTextColumn(
+    String name,
+    String tableName,
+    bool nullable, {
+    this.minTextLength,
+    this.maxTextLength,
+    String $customConstraints,
+    Expression<String, StringType> defaultValue,
+  }) : super(name, tableName, nullable,
+            $customConstraints: $customConstraints, defaultValue: defaultValue);
 
   @override
   Expression<bool, BoolType> like(String pattern) =>
@@ -91,8 +102,8 @@ class GeneratedTextColumn extends GeneratedColumn<String, StringType>
 
   @override
   bool isAcceptableValue(String value, bool duringInsert) {
-    final nullOk = !duringInsert || $nullable;
-    if (value == null) return nullOk;
+    // handle nullability check in common column
+    if (value == null) return super.isAcceptableValue(null, duringInsert);
 
     final length = value.length;
     if (minTextLength != null && minTextLength > length) return false;
@@ -105,9 +116,9 @@ class GeneratedTextColumn extends GeneratedColumn<String, StringType>
 class GeneratedBoolColumn extends GeneratedColumn<bool, BoolType>
     implements BoolColumn {
   GeneratedBoolColumn(String name, String tableName, bool nullable,
-      {String $customConstraints})
+      {String $customConstraints, Expression<bool, BoolType> defaultValue})
       : super(name, tableName, nullable,
-            $customConstraints: $customConstraints);
+            $customConstraints: $customConstraints, defaultValue: defaultValue);
 
   @override
   final String typeName = 'BOOLEAN';
@@ -126,10 +137,15 @@ class GeneratedIntColumn extends GeneratedColumn<int, IntType>
   @override
   final String typeName = 'INTEGER';
 
-  GeneratedIntColumn(String name, String tableName, bool nullable,
-      {this.hasAutoIncrement = false, String $customConstraints})
-      : super(name, tableName, nullable,
-            $customConstraints: $customConstraints);
+  GeneratedIntColumn(
+    String name,
+    String tableName,
+    bool nullable, {
+    this.hasAutoIncrement = false,
+    String $customConstraints,
+    Expression<int, IntType> defaultValue,
+  }) : super(name, tableName, nullable,
+            $customConstraints: $customConstraints, defaultValue: defaultValue);
 
   @override
   void writeColumnDefinition(StringBuffer into) {
@@ -147,10 +163,14 @@ class GeneratedIntColumn extends GeneratedColumn<int, IntType>
 
 class GeneratedDateTimeColumn extends GeneratedColumn<DateTime, DateTimeType>
     implements DateTimeColumn {
-  GeneratedDateTimeColumn(String $name, String tableName, bool $nullable,
-      {String $customConstraints})
-      : super($name, tableName, $nullable,
-            $customConstraints: $customConstraints);
+  GeneratedDateTimeColumn(
+    String $name,
+    String tableName,
+    bool $nullable, {
+    String $customConstraints,
+    Expression<DateTime, DateTimeType> defaultValue,
+  }) : super($name, tableName, $nullable,
+            $customConstraints: $customConstraints, defaultValue: defaultValue);
 
   @override
   String get typeName => 'INTEGER'; // date-times are stored as unix-timestamps