graql, delete query, deletion
grakn delete data, graql delete query, graql delete instances
Delete queries in Grakn.
Delete Instances of an Entity Type
To delete an instance of an entity type from the knowledge graph, we use a match clause followed by the
delete keyword and the variable to be deleted. To try the following examples with one of the Grakn clients, follows these Clients Guide.
match $p isa person, has email "firstname.lastname@example.org"; delete $p;
GraqlDelete query = Graql.match( var("p").isa("person").has("email", "email@example.com") ).delete("p");
This deletes a particular instance of the
person type with the id of
Delete Instances of a Relation Type
To delete an instance of a relation type, similar to deleting an entity type, we first
match and then
match $org isa organisation, has name "Pharos"; $emp (employer: $org, employee: $p) isa employment; delete $emp;
GraqlDelete query = Graql.match( var("org").isa("organisation").has("name", "Pharos"), var("emp").isa("employment").rel("employer", "org").rel("employee", "p") ).delete("emp");
This deletes all instances of the
employment type where the
employer is an
Delete Associations with Attributes
Attributes with the same value are shared among their owners. It's important that one understands thoroughly how attributes are defined in a Grakn knowledge graph prior to performing
delete queries on them.
To delete only the association that a thing has with an attribute, we use the
via keyword to capture and delete the relation between the owner and the owned attribute - NOT the instance of the attribute type itself, as doing so disowns the instance from any other instance that may have owned it.
match $t isa travel, has start-date 2013-12-22 via $r; delete $r;
GraqlDelete query = Graql.match( var("t").isa("travel").has("start-date", var("st"), var("r")), var("st").val(LocalDate.of(2013, 12, 22).atStartOfDay()) ).delete("r");
This looks for a
travel that owns the attribute
start-date with the value of
2013-12-22, captures the association between the attribute and the owner as the variable
$r and finally deletes
$r. This ensures that the attribute instance of type
start-date and value
2013-12-22 remains associated with any other instance that may own it.
If we had instead written the query as
match $t isa travel, has start-date $st; $st == 2013-12-22"; delete $st;, we would have deleted the instance of
start-date with value
2013-12-22 and its association with all other concept types that previously owned it.
delete query preceded by a
match clause is used to delete one or more data instances from the knowledge graph.
Next, we learn how to update data in a Grakn knowledge graph.