Expression<D> class abstract

Any sql expression that evaluates to some generic value. This does not include queries (which might evaluate to multiple values) but individual columns, functions and operators.

To obtain the result of an Expression, add it as a result column to a JoinedSelectStatement, e.g. through DatabaseConnectionUser.selectOnly:

 Expression<int?> countUsers = users.id.count();

 // Add the expression to a select statement to evaluate it.
 final query = selectOnly(users)..addColumns([countUsers]);
 final row = await query.getSingle();

 // Use .read() on a row to read expressions.
 final amountOfUsers = query.read(counUsers);

It's important that all subclasses properly implement hashCode and ==.

Implemented types

• FunctionParameter

Implementers

• Column
• Constant
• CustomExpression
• FunctionCallExpression
• Variable

Available Extensions

• ArithmeticAggregates
• ArithmeticBigIntExpr
• ArithmeticExpr
• BaseAggregate
• BigIntAggregates
• BooleanExpressionOperators
• ComparableExpr
• DateTimeAggregate
• DateTimeExpressions
• DriftNativeStringExtensions
• JsonExtensions
• SqlIsNull
• StringExpressionOperators

Constructors

Expression()

Constant constructor so that subclasses can be constant.

const

Properties

hashCode → int

The hash code for this object.

no setter, inherited

isLiteral → bool

Whether this expression is a literal. Some use-sites need to put parentheses around non-literals.

no setter

precedence → Precedence

The precedence of this expression. This can be used to automatically put parentheses around expressions as needed.

no setter

runtimeType → Type

A representation of the runtime type of the object.

no setter, inherited

Methods

caseMatch<T>({required Map<Expression<D>, Expression<T?>> when, Expression<T?>? orElse}) → Expression<T?>

A CASE WHEN construct using the current expression as a base.

cast<D2>() → Expression<D2>

Generates a CAST(expression AS TYPE) expression.

dartCast<D2>() → Expression<D2>

Casts this expression to an expression of D.

equals(D compare) → Expression<bool>

Whether this column is equal to the given value, which must have a fitting type. The compare value will be written as a variable using prepared statements, so there is no risk of an SQL-injection.

equalsExp(Expression<D> compare) → Expression<bool>

Whether this expression is equal to the given expression.

findType(SqlTypeSystem types) → SqlType<D>

Finds the runtime implementation of D in the provided types.

isIn(Iterable<D> values) → Expression<bool?>

An expression that is true if this resolves to any of the values in values.

isInQuery(BaseSelectStatement select) → Expression<bool?>

An expression checking whether this is included in any row of the provided select statement.

isNotIn(Iterable<D> values) → Expression<bool?>

An expression that is true if this does not resolve to any of the values in values.

isNotInQuery(BaseSelectStatement select) → Expression<bool?>

An expression checking whether this is not included in any row of the provided select statement.

noSuchMethod(Invocation invocation) → dynamic

Invoked when a nonexistent method or property is accessed.

inherited

toString() → String

A string representation of this object.

inherited

writeAroundPrecedence(GenerationContext context, Precedence precedence) → void

Writes this expression into the GenerationContext, assuming that there's an outer expression with precedence. If the Expression.precedence of this expression is lower, it will be wrap}ped in

writeInner(GenerationContext ctx, Expression inner) → void

If this Expression wraps an inner expression, this utility method can be used inside writeInto to write that inner expression while wrapping it in parentheses if necessary.

writeInto(GenerationContext context) → void

Writes this component into the context by writing to its GenerationContext.buffer or by introducing bound variables. When writing into the buffer, no whitespace around the this component should be introduced. When a component consists of multiple composed component, it's responsible for introducing whitespace between its child components.

inherited

Operators

operator ==(Object other) → bool

The equality operator.

inherited