{"id":5155,"date":"2019-01-25T11:17:17","date_gmt":"2019-01-25T10:17:17","guid":{"rendered":"https:\/\/monodes.com\/predaelli\/?p=5155"},"modified":"2019-02-21T13:56:11","modified_gmt":"2019-02-21T12:56:11","slug":"multiple-fields-primary-keys-in-django","status":"publish","type":"post","link":"https:\/\/monodes.com\/predaelli\/2019\/01\/25\/multiple-fields-primary-keys-in-django\/","title":{"rendered":"Multiple fields primary keys in Django"},"content":{"rendered":"\n

I’m developing a little application in Django. <\/p>\n\n\n\n

Having developed a subtle dislike for UUIDs used as primary keys I tend to rely of the “natural keys” which are almost always identificable in a data model.<\/p>\n\n\n\n

Often thought those keys span over several fields. Think about a receipt of a multi-store multi-cashier store, their receipts are identificable by the tupla <store_id, cashier_id, date, progressive_number<\/code>>.<\/p>\n\n\n\n

It seems that Django currently does not allow<\/a>, at least out-of-the-box to use several fields grouped into a tuple as primary key. It’s also explained in its FAQs<\/a>:<\/p>\n\n\n\n


Do Django models support multiple-column primary keys?\u00b6<\/a>
No. Only single-column primary keys are supported.
But this isn\u2019t an issue in practice, because there\u2019s nothing stopping you from adding other constraints (using the unique_together<\/code> model option or creating the constraint directly in your database), and enforcing the uniqueness at that level. Single-column primary keys are needed for things such as the admin interface to work; e.g., you need a simple way of being able to specify an object to edit or delete. <\/p><\/blockquote>\n\n\n\n

So I understand why lazy developers use UUIDs.<\/p>\n\n\n\n

Simone Federici<\/a> has written django-compositekey<\/a><\/strong> but AFAICS it support only Django 1.x and not the current 2.x
It seems I have to maintain uniqueness django-way and I don’t like it the way it is: it looks like an ugly kludge.<\/p>\n\n\n\n

Update:<\/h2>\n\n\n\n

I’ve been busy with completely unrelated issues but I still haven’t solved this. Apparently neither Django developers as they wrote in “Multi-Column Primary Key support<\/a>“. Too bad, I’ll make up those keys composing primary key strings like "$store_id-$cashier_id-YYYY-MM-DD-$progressive_number"<\/code>. Hoping that my little hack will not still be in use in year ten thousand<\/p>\n\n\n\n\n\n\n\n



I would use a default primary key (auto field), and use the meta class property, unique_together<\/code>
class Hop(models.Model): migration = models.ForeignKey('Migration') host = models.ForeignKey(User, related_name='host_set') class Meta: unique_together = (("migration", "host"),)<\/code>
It would act as a “surrogate” primary key column.
If you really want to create a multi-column primary key, look into this app<\/a> <\/p><\/blockquote>\n\n\n\n

<\/p>\n","protected":false},"excerpt":{"rendered":"

I’m developing a little application in Django. Having developed a subtle dislike for UUIDs used as primary keys I tend to rely of the “natural keys” which are almost always identificable in a data model. Often thought those keys span over several fields. Think about a receipt of a multi-store multi-cashier store, their receipts are…<\/p>\n

Read more →<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"inline_featured_image":false,"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"activitypub_content_warning":"","activitypub_content_visibility":"","activitypub_max_image_attachments":4,"activitypub_interaction_policy_quote":"anyone","activitypub_status":"","footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[229,113],"tags":[],"class_list":["post-5155","post","type-post","status-publish","format-standard","hentry","category-django","category-python"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p6daft-1l9","jetpack-related-posts":[{"id":10654,"url":"https:\/\/monodes.com\/predaelli\/2023\/07\/23\/10654\/","url_meta":{"origin":5155,"position":0},"title":"Django-LiveView","author":"Paolo Redaelli","date":"2023-07-23","format":"link","excerpt":"Django LiveView: Framework for creating Realtime SPAs using HTML over the Wire technology django-liveview-demo.andros.dev\/","rel":"","context":"In "Python"","block_context":{"text":"Python","link":"https:\/\/monodes.com\/predaelli\/category\/python\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":5109,"url":"https:\/\/monodes.com\/predaelli\/2019\/01\/07\/stable-yet-experimental\/","url_meta":{"origin":5155,"position":1},"title":"Stable yet experimental","author":"Paolo Redaelli","date":"2019-01-07","format":false,"excerpt":"This tutorial is written for Django 2.1, which supports Python 3.5 and later From: Writing your first Django app, part 1 | Django documentation | Django I couldn't find Djiango 2 in my CentOS box. 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