Relation passed to #or must be structurally compatible. Incompatible values: [:references]

Question

I have two queries, I need an or between them, i.e. I want results that are returned by either the first or the second query.

First query is a simple where() which gets all available items.

@items = @items.where(available: true)

Second includes a join() and gives the current user's items.

@items =
  @items
  .joins(:orders)
  .where(orders: { user_id: current_user.id})

I tried to combine these with Rails' or() method in various forms, including:

@items =
  @items
  .joins(:orders)
  .where(orders: { user_id: current_user.id})
  .or(
    @items
    .joins(:orders)
    .where(available: true)
  )

But I keep running into this error and I'm not sure how to fix it.

Relation passed to #or must be structurally compatible. Incompatible values: [:references]

Answer 1

There is a known issue about it on Github.

According to this comment you might want to override the structurally_incompatible_values_for_or to overcome the issue:

def structurally_incompatible_values_for_or(other)
  Relation::SINGLE_VALUE_METHODS.reject { |m| send("#{m}_value") == other.send("#{m}_value") } +
    (Relation::MULTI_VALUE_METHODS - [:eager_load, :references, :extending]).reject { |m| send("#{m}_values") == other.send("#{m}_values") } +
    (Relation::CLAUSE_METHODS - [:having, :where]).reject { |m| send("#{m}_clause") == other.send("#{m}_clause") }
end

Also there is always an option to use SQL:

@items
  .joins(:orders)
  .where("orders.user_id = ? OR items.available = true", current_user.id)

Answer 2

You can write the query in this good old way to avoid error

@items = @items.joins(:orders).where("items.available = ? OR orders.user_id = ?", true, current_user.id)

Hope that helps!

Answer 3

Hacky workaround: do all your .joins after the .or. This hides the offending .joins from the checker. That is, convert the code in the original question to...

@items =
  @items
  .where(orders: { user_id: current_user.id})
  .or(
    @items
    .where(available: true)
  )
  .joins(:orders) # sneaky, but works! 😈

More generally, the following two lines will both fail

A.joins(:b).where(bs: b_query).or(A.where(query))  # error! 😞 

A.where(query).or(A.joins(:b).where(bs: b_query))  # error! 😞 

but rearrange as follows, and you can evade the checker:

A.where(query).or(A.where(bs: b_query)).joins(:b)  # works 😈 

This works because all the checking happens inside the .or() method. It's blissfully unaware of shennanigans on its downstream results.

One downside of course is it doesn't read as nicely.