Removes a specific named join from an Ecto query.

Parameters

• query: The Ecto query to modify
• binding_name: The named binding (atom) used in the join's :as option

Examples

query = from p in Post, 
          join: c in assoc(p, :comments), as: :comments,
          join: u in assoc(p, :user), as: :user

# Remove the comments join
drop_join(query, :comments)

Warning

As noted in the Ecto documentation, if a join is removed and its bindings were referenced elsewhere in the query (in where clauses, select statements, etc.), the bindings won't be removed, leading to a query that won't compile. Make sure to only remove join bindings that aren't used elsewhere.

join_override is similar to Ecto.Query.join/{4,5}, but can be called multiple times with the same alias.

Unlike reusable_join, which skips subsequent joins with the same alias, join_override will replace any existing join with the same alias with the new one.

This is useful when you need to join the same table multiple times with different conditions, while avoiding the "alias already exists" error from Ecto.

Note that because of this behaviour, it is mandatory to specify an alias when using this function.

Warning: this macro is a work-in-progress, and while the test suite passes it doesn't seem to produce valid queries, resulting in errors like (Postgrex.Error) ERROR 42P01 (undefined_table) missing FROM-clause entry for table "sb8" when executed.

join_preload is a helper for preloading associations using joins.

By default, Ecto preloads associations using a separate query for each association, which can degrade performance. You could make it run faster by using a combination of join/preload, but that requires a bit of boilerplate (see example below).

With EctoSparkles, you can accomplish this with just one line of code.

Example using just Ecto

import Ecto.Query
Invoice
|> join(:left, [i], assoc(i, :customer), as: :customer)
|> join(:left, [i, c], assoc(c, :account), as: :account)
|> join(:left, [i], assoc(i, :lines), as: :lines)
|> preload([lines: v, customers: c, account: a], lines: v, customer: {c, [a: account]})
|> Repo.all()

Example using join_preload

import EctoSparkles
Invoice
|> join_preload([:customer, :account])
|> join_preload([:lines])
|> Repo.all()

AKA join_preload++. It's more powerful, but it does it with more (and different!) syntax.

e.g.

proload(query, activity: [
  :verb, :boost_count, :like_count, :replied,
  # relations under object will have their aliases prefixed with object_, i.e.
  # :object_message, :object_post, :object_post_content
  # the original names will still be used for the associations.
  object: {"object_", [:message, :post, :post_content]}
])

Removes joins from an Ecto.Query that aren't referenced in other parts of the query.

This function analyzes the query and removes any join whose binding is not used in select, where, order_by, group_by, having, limit, offset, or distinct clauses.

Parameters

• query: An Ecto.Query struct to optimize

Returns

• The optimized Ecto.Query with unused joins removed

Examples

iex> import Ecto.Query
iex> query = from u in User, 
...>   join: p in Post, on: p.user_id == u.id,
...>   join: c in Comment, on: c.post_id == p.id, 
...>   where: p.published == true, 
...>   select: u
iex> remove_unused_joins(query)
#Ecto.Query<from u0 in User, join: p1 in Post, on: p1.user_id == u0.id, where: p1.published == true, select: u0>

reusable_join is similar to Ecto.Query.join/{4,5}, but can be called multiple times with the same alias.

Note that only the first join operation is performed, the subsequent ones that use the same alias are just ignored. Also note that because of this behaviour, it is mandatory to specify an alias when using this function.

This is helpful when you need to perform a join while building queries one filter at a time, because the same filter could be used multiple times or you could have multiple filters that require the same join, which poses a problem with how the filter/3 callback work, as you need to return a dynamic with the filtering, which means that the join must have an alias, and by default Ecto raises an error when you add multiple joins with the same alias.

To solve this, it is recommended to use this macro instead of the default Ecto.Query.join/{4,5}, in which case there will be only one join in the query that can be reused by multiple filters.