Add on_join_through_conflict option for ManyToMany Associations

lib/ecto/association.ex

@@ -1300,6 +1300,7 @@ defmodule Ecto.Association.ManyToMany do
   @behaviour Ecto.Association
   @on_delete_opts [:nothing, :delete_all]
   @on_replace_opts [:raise, :mark_as_invalid, :delete]
+  @on_join_through_conflict_opts [:raise, :nothing]
 
   defstruct [
     :field,
@@ -1312,6 +1313,7 @@ defmodule Ecto.Association.ManyToMany do
     :join_keys,
     :join_through,
     :on_cast,
+    :on_join_through_conflict,
     where: [],
     join_where: [],
     defaults: [],
@@ -1355,7 +1357,9 @@ defmodule Ecto.Association.ManyToMany do
 
     join_keys = opts[:join_keys]
     join_through = opts[:join_through]
+    on_join_through_conflict = Keyword.get(opts, :on_join_through_conflict, :raise)
     validate_join_through(name, join_through)
+    validate_on_join_through_conflict(name, on_join_through_conflict)
 
     {owner_key, join_keys} =
       case join_keys do
@@ -1431,6 +1435,7 @@ defmodule Ecto.Association.ManyToMany do
       queryable: queryable,
       on_delete: on_delete,
       on_replace: on_replace,
+      on_join_through_conflict: on_join_through_conflict,
       unique: Keyword.get(opts, :unique, false),
       defaults: defaults,
       where: where,
@@ -1554,8 +1559,9 @@ defmodule Ecto.Association.ManyToMany do
           owner_value = dump!(:insert, join_through, owner, owner_key, adapter)
           related_value = dump!(:insert, join_through, related, related_key, adapter)
           data = %{join_owner_key => owner_value, join_related_key => related_value}
+          join_table_opts = Keyword.put(opts, :on_conflict, refl.on_join_through_conflict)
 
-          case insert_join(join_through, refl, parent_changeset, data, opts) do
+          case insert_join(join_through, refl, parent_changeset, data, join_table_opts) do
             {:error, join_changeset} ->
               {:error,
                %{
@@ -1592,6 +1598,17 @@ defmodule Ecto.Association.ManyToMany do
             "an atom (representing a schema) or a string (representing a table)"
   end
 
+  defp validate_on_join_through_conflict(_name, on_join_through_conflict)
+       when on_join_through_conflict in @on_join_through_conflict_opts do
+    :ok
+  end
+
+  defp validate_on_join_through_conflict(name, other) do
+    raise ArgumentError,
+          "expected `:on_join_through_conflict` to be one of `:raise` or `:nothing` in " <>
+            "many-to-many association #{inspect(name)}, got: `#{inspect(other)}`"
+  end
+
   defp insert_join?(%{action: :insert}, _, _field, _related_key), do: true
   defp insert_join?(_, %{action: :insert}, _field, _related_key), do: true
 

lib/ecto/schema.ex

@@ -1322,6 +1322,12 @@ defmodule Ecto.Schema do
       associated records. See `Ecto.Changeset`'s section on related data
       for more info.
 
+    * `:on_join_through_conflict` - If the association is part of an insert, Ecto
+      will automatically try to create the appropriate entry in the `:join_through`
+      table. This option allows you to configure the conflict resolution behaviour
+      when the record already exists. The allowed values are `:raise` or `:nothing`.
+      Defaults to `:raise`
+
     * `:defaults` - Default values to use when building the association.
       It may be a keyword list of options that override the association schema
       or an `atom`/`{module, function, args}` that receives the association struct
@@ -2193,6 +2199,7 @@ defmodule Ecto.Schema do
     :on_delete,
     :defaults,
     :on_replace,
+    :on_join_through_conflict,
     :unique,
     :where,
     :join_where,

test/ecto/repo/many_to_many_test.exs

@@ -52,13 +52,20 @@ defmodule Ecto.Repo.ManyToManyTest do
     schema "my_schema" do
       field :x, :string
       field :y, :binary
-      many_to_many :assocs, MyAssoc, join_through: "schemas_assocs", on_replace: :delete
+
+      many_to_many :assocs, MyAssoc,
+        join_through: "schemas_assocs",
+        on_replace: :delete
 
       many_to_many :where_assocs, MyAssoc,
         join_through: "schemas_assocs",
         join_where: [public: true],
         on_replace: :delete
 
+      many_to_many :on_conflict_assocs, MyAssoc,
+        join_through: "schemas_assocs",
+        on_join_through_conflict: :nothing
+
       many_to_many :schema_assocs, MyAssoc,
         join_through: MySchemaAssoc,
         join_defaults: [public: true]
@@ -70,6 +77,10 @@ defmodule Ecto.Repo.ManyToManyTest do
       many_to_many :mfa_schema_assocs, MyAssoc,
         join_through: MySchemaAssoc,
         join_defaults: {__MODULE__, :send_to_self, [:extra]}
+
+      many_to_many :on_conflict_schema_assocs, MyAssoc,
+        join_through: MySchemaAssoc,
+        on_join_through_conflict: :nothing
     end
 
     def send_to_self(struct, owner, extra) do
@@ -107,10 +118,39 @@ defmodule Ecto.Repo.ManyToManyTest do
     assert assoc.inserted_at
     assert_received {:insert, _}
 
-    assert_received {:insert_all, %{source: "schemas_assocs"},
+    assert_received {:insert_all, %{source: "schemas_assocs", on_conflict: {:raise, [], []}},
                      [[my_assoc_id: 1, my_schema_id: 1]]}
   end
 
+  test "handles assocs on insert with on_join_through_conflict and binary join_through" do
+    sample = %MyAssoc{x: "xyz"}
+
+    changeset =
+      %MySchema{}
+      |> Ecto.Changeset.change()
+      |> Ecto.Changeset.put_assoc(:on_conflict_assocs, [sample])
+
+    TestRepo.insert!(changeset)
+    assert_received {:insert, _}
+
+    assert_received {:insert_all, %{source: "schemas_assocs", on_conflict: {:nothing, [], []}},
+                     [[my_assoc_id: 1, my_schema_id: 1]]}
+  end
+
+  test "handles assocs on insert with on_join_through_conflict and schema join_through" do
+    sample = %MyAssoc{x: "xyz"}
+
+    changeset =
+      %MySchema{}
+      |> Ecto.Changeset.change()
+      |> Ecto.Changeset.put_assoc(:on_conflict_schema_assocs, [sample])
+
+    TestRepo.insert!(changeset)
+    assert_received {:insert, _}
+
+    assert_received {:insert, %{source: "schemas_assocs", on_conflict: {:nothing, [], []}}}
+  end
+
   test "handles assocs on insert preserving parent schema prefix" do
     sample = %MyAssoc{x: "xyz"}