Active Model Value Type¶ ↑

Initializes a type with three basic configuration settings: precision, limit, and scale. The Value base class does not define behavior for these settings. It uses them for equality comparison and hash key generation only.

Type casts a value from user input (e.g. from a setter). This value may be a string from the form builder, or a ruby object passed to a setter. There is currently no way to differentiate between which source it came from.

The return value of this method will be returned from ActiveRecord::AttributeMethods::Read#read_attribute. See also: Value#cast_value.

value The raw input, as provided to the attribute setter.

Determines whether a value has changed for dirty checking. old_value and new_value will always be type-cast. Types should not need to override this method.

Determines whether the mutable value has been modified since it was read. Returns false by default. If your type returns an object which could be mutated, you should override this method. You will need to either:

• pass new_value to Value#serialize and compare it to raw_old_value

or

• pass raw_old_value to Value#deserialize and compare it to new_value

raw_old_value The original value, before being passed to deserialize.

new_value The current value, after type casting.

Converts a value from database input to the appropriate ruby type. The return value of this method will be returned from ActiveRecord::AttributeMethods::Read#read_attribute. The default implementation just calls Value#cast.

value The raw input, as provided from the database.

Returns the Arel node used for the attribute side of a where predicate. Only called when Value#transforms_query_predicates? returns true. The default implementation returns the attribute unchanged. Override this method to wrap the column reference, for example in a SQL function call.

attribute The Arel attribute for the column being compared.

Returns the Arel node used for the value side of a where predicate. Only called when Value#transforms_query_predicates? returns true. The default implementation returns a bind parameter for value. Override this method to wrap the bind parameter, for example in a SQL function call.

attribute The Arel attribute for the column being compared.

value The value being compared against, before type casting.

predicate_builder The ActiveRecord::PredicateBuilder building the predicate. Call predicate_builder.build_bind_attribute to create a bind parameter for value.

Returns true if this type can convert value to a type that is usable by the database. For example a boolean type can return true if the value parameter is a Ruby boolean, but may return false if the value parameter is some other object.

Casts a value from the ruby type to a type that the database knows how to understand. The returned value from this method should be a String, Numeric, Date, Time, Symbol, true, false, or nil.

Returns true if the type customizes how attributes and values are rendered in hash-based where predicates. When this method returns true, equality, array (IN), and range (BETWEEN) predicates are built by passing the attribute through Value#query_attribute and each value through Value#query_value. Returns false by default. Types whose read-side SQL differs from what cast and serialize produce (e.g. a UUID stored as binary comparing as id = UUID_TO_BIN(?)) should override this method to return true.

Returns the unique type name as a Symbol. Subclasses should override this method.

Convenience method for types which do not need separate type casting behavior for user and database inputs. Called by Value#cast for values except nil.