How to know existing children of an entity in Google App Engine (python)?

Question

I made entities in parent-child relationship:

# Create Employee entity
employee = Employee()
employee.put()

# Set Employee as Address entity's parent directly...
address = Address(parent=employee)

# ...or using its key
e_key = employee.key()
address = Address(parent=e_key)

# Save Address entity to datastore
address.put()

Then, suppose that we only know the address entity and want to get the parent (employee). we can get address' parent:

address.key().parent()

However, I do not know how to get the employee's child when I know employee only. I found that Key.from_path(...) method was for getting Key from parent-child relationship, but I do not know how to deal with.

Currently I think it is not possible to query children from parent. — specialscope, May 17 '12 at 09:31
I do see Python in your question, still pasting this link to something similar in Java, if you could implement something similar: http://stackoverflow.com/questions/528650/google-app-engine-query-not-filter-for-children-of-an-entity — mhan, May 17 '12 at 10:41

score 1 · Accepted Answer · edited May 18 '12 at 06:42

1

You can query for (direct or indirect) children using the .ancestor() query filter, like this:

  addresses = Address.all().ancestor(emp).fetch()

edited May 18 '12 at 06:42

systempuntoout

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answered May 18 '12 at 06:02

Nick Johnson

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it it faster than just storing parent's id in a child's column and fetch by equality of that column to id? – Michael Kariv Dec 23 '13 at 07:14

How to know existing children of an entity in Google App Engine (python)?

1 Answers1