Parent-child relationships
Similar to nested types, parent-child relationships also allow you to relate different entities together but they differ in the implementation and behavior. Unlike nested documents, they are not present within the same document, rather parent-child documents are completely separate documents. They follow the one to many relationship principle and allow you to define one type as parent and one or more as the child type.
Creating parent-child mappings
To create a parent-child mapping, you just need to specify which type should be the parent of the child type. You do not need to define anything extra in the parent type mapping but before indexing the data in the child type, you need to specify in the child's mapping who will be its parent.
Let's create a new index, twitter_parent_child:
PUT /twitter_parent_child
Now, put the mapping of the tweets type by specifying that the user will be its parent. This is done using the _parent keyword inside the mapping, but outside...
