provide a way to prevent database queries on model objects
|Reported by:||Chris Jerdonek||Owned by:||Raúl Cumplido|
|Component:||Database layer (models, ORM)||Version:||master|
|Severity:||Normal||Keywords:||model, queryset, defer, only|
|Cc:||chris.jerdonek@…, raulcumplido@…||Triage Stage:||Accepted|
|Has patch:||no||Needs documentation:||no|
|Needs tests:||no||Patch needs improvement:||no|
This is a feature request to provide a way to prevent database queries from happening in a block of code, especially on model objects (e.g. using a context manager, or an internal flag on model objects).
The motivation is for use with the QuerySet method `only()`, for example. (The
only() method is used to prevent unnecessary fields from being loaded from a database when querying.) Consider the case of using
only() to retrieve a list of many model objects, and then subsequently displaying them. If one executes some Django code after obtaining this list (e.g. by looping through the list of objects), it would be bad if this later code accidentally accessed some other field on each object. This could trigger the unintentional execution of many individual database queries (e.g. on a production database), with potentially bad consequences. I don't currently know an easy way to prevent this.
It would be good to have such a way. For example, Django could provide some sort of
noQuery() context manager which would raise an exception if the database were queried inside it. Code after the
only() line could be included in such a context manager. This could prevent accidentally hammering a database.
Alternatively, the QuerySet API could expose a way to return objects with some sort of
no_query flag set. If attribute access on such a model object required a database query, objects with such a flag set could instead raise an exception. This would also suffice to prevent accidental queries.
Change History (4)
comment:3 Changed 23 months ago by
|Owner:||changed from nobody to Raúl Cumplido|
|Status:||new → assigned|