CODEWITHSUNDEEP
postgresqlapache-age
Muhammad Zahid
Muhammad Zahid

Reputation: 129

How do I get all Child Lables of a Parent Label

I am working on Apache AGE, and I want all the child labels of a given Parent Label.
Example:
I have an edge named PARENT, and GRANDCHILD, CHILD inherits this PARENT. I want all the edges which inherit PARENT from the PostgreSQL table. Given I have the OID of PARENT edge Label available. I want to get all the OIDs of the child labels.

What I have done so FAR:

SELECT * FROM create_elabel('test', 'PARENT'); -- Created an edge Label named PARENT
SELECT * FROM create_elabel('test', 'CHILD', ARRAY['PARENT']); -- Created an edge Label named CHILD, Inherits PARENT
SELECT * FROM create_elabel('test', 'GRANDCHILD', ARRAY['PARENT']); -- Created an edge Label named GRANDCHILD, Inherits PARENT

Now In code I want the OIDs of CHILD and GRANDCHILD when I look for children of PARENT.
Which PostgreSQL function would allow me to do that?

Upvotes: 1

Views: 106

Answers (1)

Matheus Farias
Matheus Farias

Reputation: 715

You can use the find_inheritance_children function, which is going to return a list of the child label tables OID. Also, it is necessary to check before if the current label has child edges, using the has_subclass function. The has_subclass function receives a Relation type argument and will return a boolean (True if there exists a child edge or False if it doesn't). Assuming that you already have the OID of the parent label, the code must be something like:

// add this to use the functions.
#include "catalog/pg_inherits.h"

List *child_edges_oid;

// verify if the current edge has child edges
if (has_subclass(edge_label_table_oid))
{

    // get the edge's child labels OIDs 
    child_edges_oid = find_inheritance_children(edge_label_table_oid, NoLock);
}

Upvotes: 1

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