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Extension clauses

Foreach

FOREACH iterates over a list of elements. Each element is stored inside a variable which can optionally be used inside the update clauses. All update clauses are executed per iteration of the list.

  FOREACH ( <variable name> IN <expression> | <update clauses> )
OptionDescription
variable nameThe variable name that stores each element
expressionAny expression that results in a list
update clausesOne or more Cypher update clauses: SET, REMOVE, CREATE, MERGE, DELETE including FOREACH extension

It must be noted that if the result <expression> is null, then FOREACH will not fail but rather skip the execution of <update clauses> altogether.

Examples:

  FOREACH ( i IN [1, 2, 3] | CREATE (n {id : i}) )

Creates 3 nodes, each with the id property set to 1, 2 and 3 respectively.

  CREATE (n { prop : [[1, 2], [3, 4]]);

MATCH (n) FOREACH ( inner_list IN n.prop | FOREACH ( j IN inner_list | CREATE (u { prop : j }) ) );

Creates 4 nodes, each with the id property set to 1, 2, 3 and 4 respectively.

note

Similarly, the rest of the clauses mentioned in the table above can be used.

One more important detail of FOREACH, is that it supports shadowing of variables names. For example, the query below:

  CREATE (n { prop : 0 });

MATCH (n) FOREACH ( i IN [1] | FOREACH ( i IN [3] | SET n.prop = i ) );

will end up setting the property prop of the created node to 3.