Reduce number of queries to database for model_delta function
#256
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When field is a relation `get_field_value` requires at least 2 additional queries to database. If __str__ method of related object contains further relations, much more queries might be required. Accessing internal attribute (`field.attname`, usually `f'{field.name}_id'`), however, doesn't require any additional database queries. Only when `model_delta` determines the field really changed, string representation of the related objects are obtained by querying database. This can increase time needed to save lots of objects (>100) in the same view, when these objects have many relations, but not many (if any) of them changed.
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When field is a relation
get_field_valuerequires at least 2 additional queries to database. If str method of related object contains further relations, much more queries might be required. Accessing internal attribute (field.attname, usuallyf'{field.name}_id'), however, doesn't require any additional database queries. Only whenmodel_deltadetermines the field really changed, string representation of the related objects are obtained by querying database. This can increase time needed to save lots of objects (>100) in the same view, when these objects have many relations, but not many (if any) of them changed.