DB Model Query¶

Registering Hooks¶

The neutron_lib.db.model_query.register_hook function allows hooks to be registered for invocation during a respective database query.

Each hook has three components:

• “query”: used to build the query expression

• “filter”: used to build the filter expression

• “result_filters”: used for final filtering on the query result

Query hooks take as input the query being built and return a transformed query expression. For example:

def mymodel_query_hook(context, original_model, query):
    augmented_query = ...
    return augmented_query

Filter hooks take as input the filter expression being built and return a transformed filter expression. For example:

def mymodel_filter_hook(context, original_model, filters):
    refined_filters = ...
    return refined_filters

Result filter hooks take as input the query expression and the filter expression, and return a final transformed query expression. For example:

def mymodel_result_filter_hook(query, filters):
    final_filters = ...
    return query.filter(final_filters)