Add association_primary to has_and_belongs_to_many

[AndiLavera]

First, let me say if this already exists and I am using jennifer wrong, please just let me know!

What does this PR do?

Adds association_primary to has_and_belongs_to_many. Currently, the query is built by defaulting to the primary key of the other table with T.primary. This allows users to define a different column, like uuid, while keeping id as the primary key for the table.

Any background context you want to provide?

Right now i have an App & a User model. They are connected by has_and_belongs_to_many with the join table being apps_users.

App psuedo sql table:

id, integer, not null, nextval
name, string
uuid, string, unique, not null # this is what apps_users is referencing
"apps_pkey" PRIMARY KEY, btree (id)
TABLE "apps_users" CONSTRAINT "fk_cr_606d320c60" FOREIGN KEY (app_id) REFE
RENCES apps(uuid) ON UPDATE RESTRICT ON DELETE RESTRICT

apps_users sql table:

id, integer, not null, nextval
user_id, integer
app_id, string
"apps_users_pkey" PRIMARY KEY, btree (id)
FOREIGN KEY (app_id) REFERENCES apps(uuid) ON UPDATE R
ESTRICT ON DELETE RESTRICT

Right now when i do:

user = User.find 1
user.apps if user

It throws a bad query error. The sql looks like this:

SELECT apps.* FROM apps JOIN apps_users ON apps_users.app_id = apps.id AND apps_users.user_id = $1

Notice the apps_users.app_id = apps.id. A proper query would look like:

apps_users.app_id = apps.uuid

In the user class i can do association_foreign: :uuid which is obviously wrong but changes the sql query to:

apps_users.uuid = apps.id

Almost right. That's what led me down this rabbit hole. With this PR, i can change the above to association_primary: :uuid

apps_users.id = apps.uuid

Release notes

Please fill the corresponding section regarding this pull request notes below instead of modifying CHANGELOG.md file. Please remove all redundant sections before posting request.

Model
Adds association_primary to has_and_belongs_to_many relation to allow specifying a separate column for querying other than the primary key column

Other

I am not too happy with how association_primary_key came out in ManyToMany and would love to see a more elegant solution.

[imdrasil]

Great job 👍 I'd only adjust one tiny thing. This feature definitely will be useful

[AndiLavera]

Would you like me to make a spec? I haven't dug into your tests so idk what's their but i am sure this spec would be similar to whatever spec tests 'association_foreign'.

[imdrasil]

@andrewc910 It would be great

[AndiLavera]

Okay, i think i did it.

All i did was add association_primary in the Contact class for the specs and then change a spec to ensure the sql query is utilizing the new key instead of defaulting for the primary key. Please let me know if this was not correct.

I also change the association_primary method as we discussed earlier. Your recommendations caused a type error becuase T.c() can't accept Nil. What i did builds on your ternary operator recommendation.

Finally i added a comment which i plan to remove. Just wanted to mark it and see your thoughts. I couldn't quite understand the method join_condition in the ManyToMany file. I believe the T.primary should be changed to association_primary_key but i wanted to run it by you.

[AndiLavera]

Problem: When using association_primary you cannot use add_{{name.id}}(rel : Hash). This behavior happens because ManyToMany(T, Q)#add_join_table_record hardcodes the value for association_foreign_key with objects primary key.

Fix: This newest commit changes RelationDefinition#add_{{name.id}}(rel : Hash) for has_and_belongs_to_many when using association_primary. It probably also fixes add_{{name.id}}(rel : {{klass}}) but i didn't test.

New Problem: rel.to_h.transform_keys { |key| key.to_s }[association_primary]
rel is the new object like user_profile while association_primary is a string. I couldn't figure out how to get the value with a string so i converted the object to hash. I then convert the symbol keys into string and then fetch the value. There has to be a better way to access the value of an object with a string. I am hoping you have a better way somewhere in Jennifer.

**Note:**I don't believe there are explicit tests for these methods. This was something i discovered when refactoring some controllers.

[imdrasil]

association_primary ? rel.attribute(association_primary.not_nil!) : rel.primary

[imdrasil]

this is correct

[imdrasil]

Yeah, my initial suggestion does work because association_primary is a method and it's type is always resolved as String | Symbol | Nil. The right place to adjust tests is spec/model/relation_definition_spec.cr (%has_and_belongs_many section).