Made after a values() call will have its extra selected fieldsĬalling only() and defer() after values() doesn’t make If you use a values() clause after an extra() call,Īny fields defined by a select argument in the extra() mustīe explicitly included in the values() call. When using values() together with distinct(), be aware that For a distinct() call with specifiedįield names, the database will only compare the specified field names. Normal distinct() call, the database compares each field in each row whenĭetermining which rows are distinct. Translates to a SELECT DISTINCT ON SQL query. Specify the names of fields to which the DISTINCT should apply. On PostgreSQL only, you can pass positional arguments ( *fields) in order to Values() together, be careful when ordering by fields not in the The moral here is that if you are using distinct() be careful about Ordering) will still be involved and may affect uniqueness of the results. Selected, the columns used in any order_by() (or default model Similarly, if you use a values() query to restrict the columns Ordering), it sometimes looks like non-distinct results are being returned. Since the extra columnsĭon’t appear in the returned results (they are only there to support Otherwise duplicate rows appear to be distinct. Model, those fields will be added to the selected columns and they may make This can sometimes lead to unexpected results when used You can order by a field converted to lowercase withĪny fields used in an order_by() call are included in the SQL Respect to case-sensitivity, Django will order results however your database There’s no way to specify whether ordering should be case sensitive. Not, make sure the results are what you expect. Of the items you’re ordering, this approach should not present problems. You can be sure that there will only be one ordering piece of data for each Thus, take care when using multi-valued field to order the results. Were working on to begin with - which is probably neither expected nor Using order_by() on the QuerySet could return more items than you Into the new QuerySet that order_by() creates. Here, there could potentially be multiple ordering data for each Event Įach Event with multiple children will be returned multiple times CASCADE, related_name = "children", ) date = models. ForeignKey ( "self", on_delete = models. To determine how many entries have been made in each blog:Ĭlass Event ( Model ): parent = models. Everythingįor example, if you were manipulating a list of blogs, you may want That reference a single field can be anonymous arguments. The model field that is being aggregated. Generated for them based upon the name of the aggregate function and The aggregation functions that are provided by Django are describedĪnnotations specified using keyword arguments will use the keyword as To each object in the QuerySet that is returned. Reference to a field on the model (or any related models), or an aggregateĮxpression (averages, sums, etc.) that has been computed over the objects thatĪre related to the objects in the QuerySet.Įach argument to annotate() is an annotation that will be added Force evaluation of a QuerySet by calling list() onĪnnotate() ¶ annotate( * args, ** kwargs) ¶Īnnotates each object in the QuerySet with the provided list of queryĮxpressions. Django provides aĬount() method for precisely this reason. Note: If you only need to determine the number of records in the set (andĭon’t need the actual objects), it’s much more efficient to handle a countĪt the database level using SQL’s SELECT COUNT(*). This, as you might expect, returns the length of the result list. A QuerySet is evaluated when you call len() on it. Immediately see your results when using the API interactively. This is for convenience in the Python interactive interpreter, so you can A QuerySet is evaluated when you call repr() on it. Purposes of this section is that the results are read from the database. See the following section for details of what Translate well into SQL and it would not have a clear meaning either. More filters, or modifying ordering) is not allowed, since that does not Slicing a QuerySet that has beenĪlso note that even though slicing an unevaluated QuerySet returnsĪnother unevaluated QuerySet, modifying it further (e.g., adding Will execute the database query if you use the “step” parameter of slice QuerySet usually returns another unevaluated QuerySet, but Django As explained in Limiting QuerySets, a QuerySet canīe sliced, using Python’s array-slicing syntax. Support for asynchronous iteration was added.
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