Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I always assumed that chaining multiple filter calls in Django was always the same as collecting them in a single call. The first queryset with the chained filter calls joins the Inventory model twice effectively creating an OR between the two conditions whereas the second queryset ANDs the two conditions together. I was expecting that the first query would also AND the two conditions.
Is this the expected behavior or is this a bug in Django? The answer to a related question Is there a downside to using ". The way I understand it is that they are subtly different by design and I am certainly open for correction : filter A, B will first filter according to A and then subfilter according to B, while filter A. Everything inside a single filter call is applied simultaneously to filter out items matching all those requirements.
Successive filter calls further restrict the set of objects. In this second example filter A. The second filter restricted the set of blogs further to those that are also B. The entries select by the second filter may or may not be the same as the entries in the first filter. These two style of filtering are equivalent in most cases, but when query on objects base on ForeignKey or ManyToManyField, they are slightly different. Examples from the documentation.
For the 2nd query chained filters oneit filters out blog1 and blog2. The first filter restricts the queryset to blog1, blog2 and blog5; the second filter restricts the set of blogs further to blog1 and blog2. We are filtering the Blog items with each filter statement, not the Entry items.
This will cover all the results from Example 1, but it will generate slightly more result.
Learn more. Chaining multiple filter in Django, is this a bug?Sap bom badi
Ask Question. Asked 8 years, 5 months ago. Active 11 months ago. Viewed 84k times. Equivalent Model. ForeignKey Book class Profile models. OneToOneField auth. Active Oldest Votes. Successive filter calls further restrict the set of objects Anupam This behavior, although documented, seems to violate the principle of least astonishment. Multiple filter 's AND together when fields are on the same model, but then OR together when spanning relationships.
This makes sense when you look at the queries generated in the question - the. This answer is incorrect.Django ORM Object-relational mapping makes querying the database so intuitive, that at some point you might forget that SQL is being used in the background.
This particularity is especially relevant when you are creating your QuerySets dynamically. Here it is. I won't discuss whether that's a Django bug or a feature, but these are my observations about it. Let's create an app with books and authors, where each book can be written by multiple authors. The similar app with sample data can be found in this repository.
With the above models, you could define the following QuerySet to select books which author is me, Aidas Bendoraitis. We can check what SQL query it would generate with str queryset. On the other hand, if you are defining query expressions in the same filter method like this:. Here the empty Q doesn't have any impact for the generated SQL query, so you don't need the complexity of creating a list of filters and then joining all of them with the bitwise AND operator, like this:.
Cover photo by Tobias Fischer. Post a Comment. The Books and Authors Example Let's create an app with books and authors, where each book can be written by multiple authors. Posted by Aidas Bendoraitis a. No comments:. Newer Post Older Post Home. Subscribe to: Post Comments Atom.By using Conditional Expressions we can use "If Else" expressions while querying the database.
Conditional expressions executes series of conditions while querying the database, It checks the condition for every record of the table in database and returns the matching results.
The following are the Conditional Expressions in Django and Consider the below model for sample queries. A Case expression is like the if It executes the conditions one by one until one of the given conditions are satisfied. If no conditions are satisfied then the default value is returned if it is provided otherwise "None" will be returned.
It hits the database only one time. So, We can reduce the no of queries to the database. By reducing the number of queries on the database, ultimately we can improve the efficiency and response time. Django-blog-it : django blog with complete customization and ready to use with one click installer Edit. Nowadays, people are using wildcard domains to provide same user experience across different domains. Using subdomains, we can be able to host multiple sites with ….
Users can't remember these details and, …. This blog explains you how to use Token Authentication to authenticate users within a Django Application.
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Sorl thumbnail is the package which is being widely used to generate thumbnail in Django.This module is meant to be as quick to integrate as possible, and thus extensive customization will likely benefit from a fork.
That said, a number of options are available. Currently, the app allows for. Take a look at the requirements.
Configuration is minimal for termsandconditions itself, A quick guide to a basic setup is below, take a look at the demo app for more details. By default, some pages are excluded from the middleware, you can configure exclusions with these settings:. This can be particularly useful for i18n, where your url could get prepended with a language code. A numeric value is the number of seconds that the terms and their acceptance should be cached default If set to 0, values will never be cached.
Thus, instead of using e. The template tag will take care that a proper modal is shown to the user informing a user that new terms have been set and need to be accepted. To use the template tag, do the following. In your template for example in base. This will ensure that on every page using the template that is on each page using base.
The modal will show the basic information about the new terms as well as a link to page which enables the user to accept these terms. Please note that a user may wish not to accept terms and close the modal. In such a case, the modal will be shown again as soon as another view with the template including the template tag is called.
When needed e. If you happen to use termsandconditions which text field includes some template tags e. Note, that you need to modify the default termsandconditions templates, as the default ones use terms as template variable.
Note that the configuration above also prevents django-socialauth from updating profile data from the social backends once a profile is created, due to:. This is wise behavior when you are letting users update their own profile details. In case of django-modeltranslation the setup is rather straight forward, but needs several steps.
Here they are. In your settings. As we switch to the local migration for the termsandconditions module, we need to execute initial migration for the module as a starting point. Now, just execute the migration:. To translate terms-and-conditions model to other languages as specified in settings. This assumes you want to have 3 most relevant model fields translated.Antacid classification
After that you just need to make migrations again to account for new fields due to modeltranslation :. Your model is now ready to cover the translations! Just as hint we suggest to also include some data migration in order to populate newly created, translated fields i.
Modify your settings. Make initial local migration 3.Miraculous ladybug season 3 episode 11 english dub
Add translation. Contributors: Tim White tim cyface.Q objects provides you complete control over the where clause of the query.Neway valve seat cutter
If you want to OR your conditions. If you want to AND your conditions. Django ORM Cookbook. Introduction 1. How to find the query associated with a queryset? How to do a NOT query in Django queryset? How to do union of two querysets from same or different models? How to select some fields only in a queryset?
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How to do a subquery expression in Django? How to filter a queryset with criteria based on comparing their field values 9. How to filter FileField without any file? How to perform join operations in django ORM? How to find second largest record using Django ORM? Find rows which have duplicate field values How to find distinct field values from queryset?
How to use Q objects for complex queries?
How to group records in Django ORM? How to efficiently select a random object from a model? How to use arbitrary database functions in querysets?
How to create multiple objects in one shot? How to copy or clone an existing model object? How to ensure that only one object can be created? How to update denormalized fields in other models on save? How to perform truncate like operation using Django ORM?
What signals are raised by Django during object creation or update? How to convert string to datetime and store in database? How to order a queryset in ascending or descending order?
How to order a queryset in case insensitive manner? How to order on two fields 4. How to order on a field from a related model with a foreign key? How to order on an annotated field? How to model one to one relationships? How to model one to many relationships? How to model many to many relationships? How to include a self-referencing ForeignKey in a model 5. How to convert existing databases to Django models?The root QuerySet provided by the Manager describes all objects in the database table.
Usually, though, you'll need to select only a subset of the complete set of objects.
Conditions on django filter backend in django rest framework?
The default behavior of REST framework's generic list views is to return the entire queryset for a model manager. Often you will want your API to restrict the items that are returned by the queryset. The simplest way to filter the queryset of any view that subclasses GenericAPIView is to override the. Overriding this method allows you to customize the queryset returned by the view in a number of different ways.
Django Conditional Expressions in Queries
You might want to filter the queryset to ensure that only results relevant to the currently authenticated user making the request are returned. You could then write a view that returned a purchase queryset filtered by the username portion of the URL:. A final example of filtering the initial queryset would be to determine the initial queryset based on query parameters in the url. We can override. As well as being able to override the default queryset, REST framework also includes support for generic filtering backends that allow you to easily construct complex searches and filters.
For example. You can also set the filter backends on a per-view, or per-viewset basis, using the GenericAPIView class-based views. Note that if a filter backend is configured for a view, then as well as being used to filter list views, it will also be used to filter the querysets used for returning a single object.
For instance, given the previous example, and a product with an id ofthe following URL would either return the corresponding object, or return a response, depending on if the filtering conditions were met by the given product instance:. Note that you can use both an overridden. For example, if Product had a many-to-many relationship with Usernamed purchaseyou might want to write a view like this:.
To use DjangoFilterBackendfirst install django-filter. This will automatically create a FilterSet class for the given fields, and will allow you to make requests such as:. For more advanced filtering requirements you can specify a FilterSet class that should be used by the view. You can read more about FilterSet s in the django-filter documentation. It's also recommended that you read the section on DRF integration.
The SearchFilter class supports simple single query parameter based searching, and is based on the Django admin's search functionality.Enti locali in rete: lanagrafica dellamministrazione emiliano
By default, searches will use case-insensitive partial matches. If multiple search terms are used then objects will be returned in the list only if all the provided terms are matched. For more details, see the Django documentation. The OrderingFilter class supports simple query parameter controlled ordering of results. It's recommended that you explicitly specify which fields the API should allowing in the ordering filter.The following are the core arguments that apply to all filters.JSON - Dynamic Dependent Dropdown List using Jquery and Ajax
Note that they are joined to construct the complete lookup expression that is the left hand side of the ORM. The name of the model field that is filtered against. The field lookup that should be performed in the filter call. Defaults to exact.
An optional argument that tells the filter how to handle the queryset. It can accept either a callable or the name of a method on the FilterSet. The callable receives a QuerySetthe name of the model field to filter on, and the value to filter with. It should return a filtered Queryset.
Note that the value is validated by the Filter. A boolean that specifies whether the Filter will use distinct on the queryset.
How to perform OR condition in django queryset?
This option can be used to eliminate duplicate results when using filters that span relationships. Defaults to False. A boolean that specifies whether the Filter should use filter or exclude on the queryset. A boolean that specifies whether the Filter is required or not.
Any additional keyword arguments are stored as the extra parameter on the filter. They are provided to the accompanying form Field and can be used to provide arguments like choices. Some field-related arguments:. The django. In addition to the widgets that are included with Django that you can use there are additional ones that django-filter provides which may be useful:.
This filter does simple character matches, used with CharField and TextField by default. This filter matches UUID values, used with models. UUIDField by default. This filter matches values in its choices argument. The choices must be explicitly passed when the filter is declared on the FilterSet. For example. ChoiceFilter also has arguments that enable a choice for not filtering, as well as a choice for filtering by None values.
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