There is a scenario where I want to store two types of information for a field. For example, consider a field namely "name". This field should two types of the following information:-
Boolean - to store whether the user wants this field to be shown or not.
Label - if the user wants to change the label to show.
I was wondering to solve this by using a model. Any suggestions?
You can define fields on other model and use them with genericForeignKey
Related
I have several times come across a want to have a Django model field that comprises multiple database columns, and am wondering what the most Django way to do it would be.
Three use cases come specifically to mind.
I want to provide a field that wraps another field, keeping record of whether the wrapped field has been set or not. A use case for this particular field would be for dynamic configuration. A new configuration value is introduced, and a view marks itself as dependent upon a configuration value, redirecting if the value isn't set. Storing whether it's been set yet or not allows for easy indefinite caching of the state. This also lets the configuration value itself be not-nullable, and the application can ignore any value it might have when unset.
I want to provide a money field that combines a decimal (or integer) value, and a currency.
I want to provide a file field with a link to some manner of access rule to determine whether the request should include it/a request for it should succeed.
For each of the use cases, there exists a workaround, that in each case seems less elegant.
Define the configuration fields as nullable. This is undesirable for a few reasons: it removes the validity of NULL as a value for the configuration itself, so tristates and other use valid cases for NULL have to become a pair of fields or a different data type, or an edge case; null=True on the fields allows them to be set back to None in modelforms and the admin without writing a custom FormField for them every time; and every nullable column in a database is arguably bad design.
Define the field as a subclass of DecimalField with an argument accepting a string, and use that to contribute another field to the model. (This is what django-money does). Again, this is undesirable: fields are appearing "as if by magic" on the model; and configuring the currency field becomes not obvious.
Define the combined file+rule field instead as an entire model, and one-to-one to it from the model where you want to have the field. This is a solution to all use cases, but again comes with downsides: there's an extra JOIN required for every instance of the field - one can imagine a User with profile_picture, cv, passport, private_key etc.; there's an implicit requirement to .select_related(*fields) on every query that would ever want to access the fields; and the layout of the related model is going to have cold data interleaved with hot data all over the place given that it's reused everywhere.
In addition to solution 3., there's also the option to define a mixin factory that produces the multiple fields with matching names and whatever desired properties and methods. Again this isn't perfect because the user ends up with fields being defined in the model body, but also above that in the inheritance list.
I think the main reason this keeps sending me in circles is because custom Django model fields are always defined in terms of a single base field, because it's done by inheritance.
What is the accepted way to achieve this end?
In my project few models has many fields like more than 25. Like i have a model name PeriodOfStay. and it fields are like
date_of_entry
i94_number
port_of_entry
city ....etc (please check the image for all field)
also it has many boolean fields . in one form user can multiple options.
most of the fields are optional.
so i am confused should i put all the fields in one model. Is it best practice. I don't want split one model to more and use OneToOne Relation cause in that case i need to break up many models cause most of the models in my project are like this also i need to send all data at once in a single request.
I just need to save data and show data to user. in some case i need to search by some field . Like in this form i need to search by i94_number.
Is using JsonField is ok for this problem cause i need to search & filter in some case.
I appreciate any help. Advance Thanks For Help.
Regarding your question about when to use one-to-one relations:
https://dba.stackexchange.com/a/15405
I think a JsonField is not what you want if you want to search & filter based on some fields. Keeping it in normal fields will make it faster
Some related resource that might be interesting: https://en.wikipedia.org/wiki/Database_normalization
How can I make a field that can accept more than one input and connect it to my database?
For example : I want to make a field that is called 'user_skills' and the user can enter more than skil in that field .. How can I do that?
Depends on the Database you are using. If you are using postgresSql you can do this with ArrayField link
Other possible options can be use JsonField or try to use normalize Model where you can store pre-define value's of corresponding field and can access them with ManyToManyField.
Preface
I need to have objects (Object model) with an individual set of fields (Field model). It contains name and type (see the diagram). Each connection between Object and Field stores the field's value. Datatype of value depends on the Field type property and physically the value will be stored in one of the predefined db columns (value_number, value_text, ...).
How I want it to work:
field = Field.objects.get(pk=1)
sought_for = Object.fields.filter(field=field, value='test')
Is there a way to create such a field that can be put to QuerySet just as simple as in the example but it actually, depending on the field's type, uses different db column or even columns as I suppose that in the future there will types that involve more than one column to store its value.
P.S. I tried some EAV applications but they seemed to be too complicated for my case.
The diagram:
Field model, it stores name and type of fields
FieldValue, the model the values for the fields are stored.
UPD: Eventually I came to a thought that the very approach to use Postgres (or any relational database) is not the best choice. I got this implemented easily in MongoDB.
I got a model with 2 fields: latitude and longitude. Right now they're 2 CharFields, but I want to make a custom widget to set it in admin - was thinking about displaying Google Maps, then getting the coordinates of the marker.
But can I have 1 widget (a single map) to set 2 different fields?
Define lat and long fields on your form; set them to use the HiddenInputWidget.
After the init of your form, add another field which contains your custom widget that takes two values.
In the clean method for that added field, set the values of self.cleaned_data['lat'] and self.cleaned_data['lng']
There are probably cleaner ways, but it should work
I've used overriden full_clean method for data splitting. Using clean_FIELD method is too late.
I ended up setting a custom form on my admin with an extra not required field which had a widget that controls the map and setting a maps widget of that like stevejalim. However I didn't hide the input fields since they were still left in the view and I don't mind seeing them. It would probably be cleaner to override the template for editing that model instead and putting in a map, but that seemed like to much work for something that should be simple.
One solution would be if Django allowed for complex model fields where one model field corresponds to multiple db columns but that's not yet supported (see https://code.djangoproject.com/ticket/5929)
The other would be if Django would let us use a form field that corresponds to two model fields, but there doesn't seem to be a way of accomplishing that and I can't find a ticket for it.