Rails find or create by more than one attribute

Question

There is a handy dynamic attribute in active-record called find or create by   Model find or create by  lt attribute gt    lt attribute gt    gt       But what if I need to find or create by more than one attribute   Say I have a model to handle a M M relationship between Group and Member called GroupMember  I could have many instances where member id   4  but I don t ever want more than once instance where member id   4 and group id   7  I m trying to figure out if it s possible to do something like this   GroupMember find or create  member id   gt  4   group id   gt  7    I realize there may be better ways to handle this  but I like the convenience of the idea of find or create

User · Answer

For anyone else who stumbles across this thread but needs to find or create an object with attributes that might change depending on the circumstances, add the following method to your model:

# Return the first object which matches the attributes hash
# - or -
# Create new object with the given attributes
#
def self.find_or_create(attributes)
  Model.where(attributes).first || Model.create(attributes)
end

Optimization tip: regardless of which solution you choose, consider adding indexes for the attributes you are querying most frequently.

User · Answer

Multiple attributes can be connected with an and   GroupMember find or create by member id and group id 4  7     use find or initialize by if you don t want to save the record right away   Edit  The above method is deprecated in Rails 4  The new way to do it will be   GroupMember where  member id   gt  4   group id   gt  7  first or create   and  GroupMember where  member id   gt  4   group id   gt  7  first or initialize   Edit 2  Not all of these were factored out of rails just the attribute specific ones    https   github com rails rails blob 4-2-stable guides source active record querying md  Example   GroupMember find or create by member id and group id 4  7    became   GroupMember find or create by member id  4  group id  7

User · Answer

By passing a block to find or create  you can pass additional parameters that will be added to the object if it is created new  This is useful if you are validating the presence of a field that you aren t searching by   Assuming   class GroupMember  lt  ActiveRecord  Base     validates presence of  name end   then  GroupMember where  member id   gt  4   group id   gt  7  first or create    gm  gm name    John Doe      will create a new GroupMember with the name  John Doe  if it doesn t find one with member id 4 and group id 7

User · Answer

In Rails 4 you could do   GroupMember find or create by member id  4  group id  7    And use where is different   GroupMember where member id  4  group id  7  first or create   This will call create on GroupMember where member id  4  group id  7    GroupMember where member id  4  group id  7  create   On the contrary  the find or create by member id  4  group id  7  will call create on GroupMember   GroupMember create member id  4  group id  7    Please see this relevant commit on rails rails

User · Answer

You can do   User find or create by first name   Pen  lope   last name   Lopez   User where first name   Pen  lope   last name   Lopez   first or create   Or to just initialize   User find or initialize by first name   Pen  lope   last name   Lopez   User where first name   Pen  lope   last name   Lopez   first or initialize

[ruby-on-rails] Rails find_or_create_by more than one attribute?

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