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.
For convenience, EdgeDB provides some pre-defined constraints. Click the name of a given constraint for the full documentation.
Enforce uniqueness among all instances of the containing type | |
Custom constraint expression | |
A list of allowable values | |
Maximum value numerically/lexicographically | |
Maximum value numerically/lexicographically (exclusive range) | |
Maximum length (strings only) | |
Minimum value numerically/lexicographically | |
Minimum value numerically/lexicographically (exclusive range) | |
Minimum length (strings only) | |
Regex constraint (strings only) |
The expression
constraint is used to define custom constraint logic. Inside
custom constraints, the keyword __subject__
can used to reference the
value being constrained.
The constraint below uses the built-in len()
function, which returns
the length of a string.
type User {
required property username -> str {
# as custom constraint
constraint expression on (len(__subject__) <= 25);
# with built-in
constraint max_len_value(25);
};
}
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>
).
type ConstrainedVector {
required property x -> float64;
required property y -> float64;
constraint expression on (
.x ^ 2 + .y ^ 2 <= 25
);
}
When defining a constraint on a link, __subject__
refers to the link
itself. This is commonly used add constraints to link properties.
type User {
property name -> str;
multi link friends -> User {
single property strength -> float64;
constraint expression on (
__subject__@strength >= 0
);
}
}
Custom scalar types can be constrained.
scalar type username extending str {
constraint regexp(r'^[A-Za-z0-9_]{4,20}$');
}
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.
scalar type title extending str {
constraint expression on (
__subject__ = str_trim(__subject__)
);
}