Overview

UQL constraints enforces rules for data that can go into the current graphset. If there is any violation between the constraint and the data modification action, the action is aborted.

The following constraints are used in UQL:

• EDGE KEY: Ensures the existence of properties and the uniqueness of their values.
• NOT NULL: Ensures that a property cannot have a null value.

Creating Constraints

A constraint is created for one or multiple properties with the CREATE CONSTRAINT statement. The constraint creation is executed as a job, you may run show().job(<id?>) afterward to verify the success of the creation.

CREATE CONSTRAINT <constraintName> <ifNotExistsFlag?>
FOR <aliasDecl>
REQUIRE <alias>.<property> <constraintType>
OPTIONS {
  <item?>: {<key?>: <value?>}
}

Details

• <constraintName> is the unique name provided for the constraint. The creation will fail if a constraint with the same name already exists.
• With the optional <ifNotExistsFlag?>, i.e., IF NOT EXISTS, if the specified <constraintName> already exists, or if a constraint already exists with a type that allows only one constraint, no creation will occur, and the operation will complete without throwing errors.
• The optional OPTIONS clause can be used to provide additional configurations.

Creating a constraint can take some time, as the system needs to scan all existing data for compliance with the constraint. The creation process will fail if any existing data does not meet the constraint. Additionally, to ensure data consistency, other data modifications are put on hold during the constraint creation process.

Once a constraint is applied to a property, any data modification that violates the constraint will result in an error.

EDGE KEY

The EDGE KEY constraint applies exclusively to edge properties. It ensures that the specified property:

• Exists for all edge schemas.
• Has unique values across the graph.
• Does not allow null values.

For a composite EDGE KEY constraint involving multiple properties, the combination of their values must be unique.

The EDGE KEY constraint creation enforces uniqueness among property values within each shard, allowing duplicates across different shards. However, any data modifications made after the EDGE KEY constraint is applied must adhere to global uniqueness.

Only one EDGE KEY constraint can be created in a graphset and it applies to all edge schemas. The EDGE KEY constraint establishes a mapping between the specified properties and _uuid of edges. Meanwhile, the properties specified by the EDGE KEY constraint are loaded to caches for query acceleration.

// Creates a single-property EDGE KEY constraint
CREATE CONSTRAINT <constraintName> <ifNotExistsFlag?>
FOR ()-[<alias>]-()
REQUIRE <alias>.<property> IS EDGE KEY
OPTIONS {
  type: {<property?>: <type?>}
}

// Creates a composite EDGE KEY constraint
CREATE CONSTRAINT <constraintName> <ifNotExistsFlag?>
FOR ()-[<alias>]-()
REQUIRE (<alias>.<property1>, <alias>.<property2>, ...) IS EDGE KEY
OPTIONS {
  type: {<property1?>: <type1?>, <property2?>: <type2?>, ...}
}

Details

• The OPTIONS clause defines the desired type for all specified properties, which must match their corresponding types in the database. If the OPTIONS clause is omitted, all edge key properties default to the string type.
• The EDGE KEY constraint does not support the following property types: decimal, list, and set.

To create an EDGE KEY constraint for edge properties named notes while the type of each notes property must be string:

CREATE CONSTRAINT edge_key
FOR ()-[e]-() REQUIRE e.notes IS EDGE KEY

To create an EDGE KEY constraint for edge properties named score while the type of each score property must be float:

CREATE CONSTRAINT edge_key
FOR ()-[e]-() REQUIRE e.score IS EDGE KEY
OPTIONS {
  type: {score: "float"}
}

To create an EDGE KEY constraint for edge properties named notes and score while the types of each notes andscore properties must be string and float respectively:

CREATE CONSTRAINT edge_key
FOR ()-[e]-() REQUIRE (e.notes, e.score) IS EDGE KEY
OPTIONS {
  type: {notes: "string", score: "float"}
}

To create an EDGE KEY constraint only if no EDGE KEY constraint currently exists, preventing an error if it does:

CREATE CONSTRAINT edge_key IF NOT EXIST
FOR ()-[e]-() REQUIRE e.notes IS EDGE KEY

NOT NULL

By default, a property can hold null values. The NOT NULL constraint enforces a property to NOT accept null values, ensuring that a value is always provided. Only one property can be specified with each NOT NULL constraint.

// Creates a NOT NULL constraint for a node property
CREATE CONSTRAINT <constraintName> <ifNotExistsFlag?>
FOR (<alias>:<schema>)
REQUIRE <alias>.<property> IS NOT NULL

// Creates a NOT NULL constraint for an edge property
CREATE CONSTRAINT <constraintName> <ifNotExistsFlag?>
FOR ()-[<alias>:<schema>]-()
REQUIRE <alias>.<property> IS NOT NULL

To create a NOT NULL constraint for the node property @user.name:

CREATE CONSTRAINT not_null_user_name
FOR (u:user) REQUIRE u.name IS NOT NULL

To create a NOT NULL constraint for the edge property @likes.weight named not_null_weight only if this name does not exist, preventing an error if it does exist:

CREATE CONSTRAINT not_null_weight IF NOT EXIST
FOR ()-[e:likes]-() REQUIRE e.weight IS NOT NULL

Showing Constriants

To retrieves information about all constraints created in the current graphset:

// Shows all constraints
show().constraint()

// Shows all constraints created for node properties
show().node_constraint()

// Shows all constraints created for edge properties
show().edge_constraint()

The information about constraints is organized into _nodeConstraint and _edgeConstraint tables. Each table includes fields that provide essential details about each constraint:

Dropping Constraints

A constraint can be dropped with the DROP CONSTRAINT statement.

DROP CONSTRAINT <constraintName> <ifExistsFlag?>

Details

• <constraintName> is the constraint name. The constraint deletion will fail if the specified name does not exist.
• With the optional <ifExistsFlag?>, i.e., IF EXISTS flag, if the specified <constraintName> is not found, no deletion will occur, and the operation will complete without throwing errors.

To drop a constraint named not_null_user_name:

DROP CONSTRAINT not_null_user_name

To drop a constraint named user_name only if it exists, preventing an error if it doesn't exist:

DROP CONSTRAINT not_null_user_name IF EXISTS

Other Restrictions

Renaming Properties

Properties with applied NOT NULL constraints can be renamed. However, renaming properties with an EDGE KEY constraint is not allowed.

Dropping Properties

A property with any applied constraints cannot be dropped until all the related constraints are removed.