Rails活动记录查询到字符串

Question

When I have the AR query like this :

MyModel.joins(:related_model).where('related_model.some_column = ?', 'somevalue')

If I used to_sql on the above code it would generate something like :

"SELECT * FROM MY_MODEL INNER JOIN RELATED_MODEL ON RELATED_MODEL.SOME_ID = MY_MODEL.SOME_ID WHERE RELATED_MODEL.SOME_COLUMN = 'SOMEVALUE'"

I'm creating a slightly, or way more complex query, and I hate to duplicate code. Is there are way that I can get this part with some command to alter the generated SQL below?

INNER JOIN RELATED_MODEL ON RELATED_MODEL.SOME_ID = MY_MODEL.SOME_ID WHERE RELATED_MODEL.SOME_COLUMN = 'SOMEVALUE'"

Answer 1

foo = MyModel.joins(:related_model).where('related_model.some_column = ?', 'somevalue').to_sql`

core_sql = foo.sub(/^SELECT * FROM MY_MODEL /,'')`

Answer 2

I think will end up needing to be a method of some sort with arrays (or a struct or hash if you want to get more complex).

Using the table_name method to access the underlying table behind a model you could do something like this.

def auto_joins (primary_model, related_models, values)
   search = primary_model + '.table_name'
   primary_table_name = eval(search)
   primary_id = primary_table_name + '_id'
   output_sql = "SELECT * FROM #{primary_table_name}"
   related_models.each do |model|
       search = model + '.table_name'
       table_name = eval(search)
       output_sql += " INNER JOIN #{table_name} ON #{table_name}.#{primary_id} = #{primary_table_name}.id "
   end
   output_sql += "WHERE 1 = 1 " #overcome no values passed in...
   values.each do |where|
        output_sql += "AND #{where}"
   end
   output_sql
end

And in my test database I had contact that had_many leads and prospects I called it like this:

auto_joins('Contact', ['Lead', 'Prospect'], ["contact.first_name = 'Brian'"])

and it generated this:

SELECT * FROM contacts 
  INNER JOIN leads ON leads.contacts_id = contacts.id  
  INNER JOIN prospects ON prospects.contacts_id = contacts.id 
  WHERE 1 = 1 AND contact.first_name = 'Brian'

If you wanted to take it further you could have a hash for {model: 'Contact', where: "first_name = 'Brian'"} and both the where and joins together based on that.

Edit Note: Evals are unsafe if you are exposing any of this to user input. You could find another way to access these models through activerecord and accomplish the same goal.