newbie trying to understand include

rubyonrails-talk
1

I have two models, users and companies as indicated below. The users table has a foreign_key "company_id".

class User < ActiveRecord::Base      has_many :companies end

class Company < ActiveRecord::Base     belongs_to: user end

In my controller:

@user = User.where(:id => params[:id]).includes(:companies)

I get the following error: SQlite3::SQLException: no such column: companies.user_id: SELECT "companies".* FROM "companies" WHERE "companies"."user_id" IN ('8')

Why is RAILS getting the foreign key wrong and why is it trying to pull columns in the users table into the companies model?

2

I have two models, users and companies as indicated below. The users table has a foreign_key “company_id”.

class User < ActiveRecord::Base has_many :companies end

class Company < ActiveRecord::Base belongs_to: user

this should be

belong_to :user

end

In my controller:

@user = User.where(:id => params[:id]).includes(:companies)

I get the following error: SQlite3::SQLException: no such column: companies.user_id: SELECT “companies”.* FROM “companies” WHERE “companies”.“user_id” IN (‘8’)

Did you create a migration and run rake db:migrate ?

Why is RAILS getting the foreign key wrong and why is it trying to pull columns in the users table into the companies model?

–

Because you used .includes it is trying to eager load the companies. If you don’t know what eager loading is, you don’t need it right now. One day you will learn what eager loading is and you will then learn to use it, but until that day you can get by without it.

If you do know what eager loading is and your intention was to use it here, that’s a different matter.

3

I have two models, users and companies as indicated below. The users table has a foreign_key "company_id".

class User < ActiveRecord::Base     has_many :companies end

class Company < ActiveRecord::Base    belongs_to: user end

In my controller:

@user = User.where(:id => params[:id]).includes(:companies)

I get the following error: SQlite3::SQLException: no such column: companies.user_id: SELECT "companies".* FROM "companies" WHERE "companies"."user_id" IN ('8')

Why is RAILS getting the foreign key wrong and why is it trying to pull columns in the users table into the companies model?

4

I did create the migration and the tables exist in the db.

If I use .joins, I have a similar error as in:

@user = User.where(:id => params[:id] ).joins(:companies)

SQLite3::SQLException: no such column: companies.user_id: SELECT "users".* FROM "users" INNER JOIN "companies" ON "companies"."user_id" = "users"."id" WHERE "users"."id" = 8

It's like something is wrong with the model associations... do I have to specify the foreign_key? It should conform to the convention.

5

FYI: I kinda of get the concept of eager loading and thought it would be better than the alternative... is there something else I need to do in order to get eager loading to work?

6

this works for me:   @user = User.where(:id => params[:id] ).joins('LEFT JOIN companies ON companies.id = users.company_id')

so then I guess its a question on understanding eager loading?

7

ERB wrote in post #1024149:

this works for me:   @user = User.where(:id => params[:id] ).joins('LEFT JOIN companies ON companies.id = users.company_id')

so then I guess its a question on understanding eager loading?

Think carefully about what you're trying to solve here. Eager loading is intended to prevent the n+1 query problem.

In the case you show here your eager loading would actually cause more queries than not using eager loading at all. You are trying to find a single user (1 SQL query), then you're trying to ask for eager loading (1+1 SQL queries). Not only have you not saved yourself anything, you actually reduced performance.

By fetching only one user object you might as well wait until some information for the associated companies are actually needed before hitting the database.

Take a look at the first example in the section on Eager Loading that you'll find a little less than half way down on the following page:

There is a very clear explanation of what eager loading is, and how it should be used.

8

erm. No it shouldn't. "belongs_to" is the correct call.

9

If you user has many companies, then Company needs the foreign key user_id to belong to user. Change your DB schema; remove the company_id field from users and add the field to companies.