Constraints​

This section assumes a basic understanding of EdgeQL.

Constraints gives users fine-grained control over which data is considered valid. The can be defined on properties, links, object types, and custom scalars.

Built-in constraints​

For convenience, EdgeDB provides some pre-defined constraints. Click the name of a given constraint for the full documentation.

The expression constraint is used to define custom constraint logic. Inside custom constraints, the keyword __subject__ can used to reference the value being constrained.

Constraints on properties​

The constraint below uses the built-in len() function, which returns the length of a string.

1. type User {
2. required property username -> str {
3. # as custom constraint
4. constraint expression on (len(__subject__) < 25);

6. # with built-in
7. constraint min_len_value(25);
8. };
9. }

Constraints on object types​

Constraints can be defined on object types. This is useful when the constraint logic must reference multiple links or properties.

Inside an object type declaration, you can omit __subject__ and simple refer to properties with the leading dot notation (e.g. .<name>).

1. type ConstrainedVector {
2. required property x -> float64;
3. required property y -> float64;

5. constraint expression on (
6. .x ^ 2 + .y ^ 2 <= 25
7. );
8. }

Constraints on links​

When defining a constraint on a link, __subject__ refers to the link itself. This is commonly used add constraints to link properties.

1. type User {
2. property name -> str;
3. multi link friends -> User {
4. single property strength -> float64;
5. constraint expression on (
6. __subject__@strength >= 0
7. );
8. }
9. }

Constraints on custom scalars​

Custom scalar types can be constrained.

1. scalar type username extending str {
2. constraint regexp(r'^[A-Za-z0-9_]{4,20}$');
3. }

Note: you can’t use exclusive constraints on custom scalar types, as the concept of exclusivity is only defined in the context of a given object type.

Use expression constraints to declare custom constraints using arbitrary EdgeQL expressions. The example below uses the built-in str_trim() function.

1. scalar type title extending str {
2. constraint expression on (
3. __subject__ = str_trim(__subject__)
4. );
5. }

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