add Ecto.Adapters.MyXQL.Constraint and delegate from the connection

integration_test/myxql/constraints_test.exs

@@ -5,8 +5,11 @@ defmodule Ecto.Integration.ConstraintsTest do
   alias Ecto.Integration.PoolRepo
 
   defmodule CustomConstraintHandler do
+    @behaviour Ecto.Adapters.SQL.Constraint
+
     @quotes ~w(" ' `)
 
+    @impl Ecto.Adapters.SQL.Constraint
     # An example of a custom handler a user might write
     def to_constraints(%MyXQL.Error{mysql: %{name: :ER_SIGNAL_EXCEPTION}, message: message}, opts) do
       # Assumes this is the only use-case of `ER_SIGNAL_EXCEPTION` the user has implemented custom errors for
@@ -194,6 +197,7 @@ defmodule Ecto.Integration.ConstraintsTest do
     assert is_integer(result.id)
   end
 
+  @tag :constraint_handler
   test "custom handled constraint" do
     changeset = Ecto.Changeset.change(%Constraint{}, from: 0, to: 10)
     {:ok, item} = PoolRepo.insert(changeset)

lib/ecto/adapters/myxql/connection.ex

@@ -5,6 +5,9 @@ if Code.ensure_loaded?(MyXQL) do
 
     @behaviour Ecto.Adapters.SQL.Connection
 
+    @impl true
+    defdelegate to_constraints(exception, options), to: Ecto.Adapters.MyXQL.Constraint
+
     ## Connection
 
     @impl true
@@ -56,46 +59,6 @@ if Code.ensure_loaded?(MyXQL) do
       end
     end
 
-    @quotes ~w(" ' `)
-
-    @impl true
-    def to_constraints(%MyXQL.Error{mysql: %{name: :ER_DUP_ENTRY}, message: message}, opts) do
-      with [_, quoted] <- :binary.split(message, " for key "),
-           [_, index | _] <- :binary.split(quoted, @quotes, [:global]) do
-        [unique: strip_source(index, opts[:source])]
-      else
-        _ -> []
-      end
-    end
-
-    def to_constraints(%MyXQL.Error{mysql: %{name: name}, message: message}, _opts)
-        when name in [:ER_ROW_IS_REFERENCED_2, :ER_NO_REFERENCED_ROW_2] do
-      with [_, quoted] <- :binary.split(message, [" CONSTRAINT ", " FOREIGN KEY "]),
-           [_, index | _] <- :binary.split(quoted, @quotes, [:global]) do
-        [foreign_key: index]
-      else
-        _ -> []
-      end
-    end
-
-    def to_constraints(
-          %MyXQL.Error{mysql: %{name: :ER_CHECK_CONSTRAINT_VIOLATED}, message: message},
-          _opts
-        ) do
-      with [_, quoted] <- :binary.split(message, ["Check constraint "]),
-           [_, constraint | _] <- :binary.split(quoted, @quotes, [:global]) do
-        [check: constraint]
-      else
-        _ -> []
-      end
-    end
-
-    def to_constraints(_, _),
-      do: []
-
-    defp strip_source(name, nil), do: name
-    defp strip_source(name, source), do: String.trim_leading(name, "#{source}.")
-
     ## Query
 
     @parent_as __MODULE__

lib/ecto/adapters/myxql/constraint.ex

@@ -0,0 +1,45 @@
+defmodule Ecto.Adapters.MyXQL.Constraint do
+  @moduledoc false
+
+  @behaviour Ecto.Adapters.SQL.Constraint
+
+  @quotes ~w(" ' `)
+
+  @impl true
+  def to_constraints(%MyXQL.Error{mysql: %{name: :ER_DUP_ENTRY}, message: message}, opts) do
+    with [_, quoted] <- :binary.split(message, " for key "),
+         [_, index | _] <- :binary.split(quoted, @quotes, [:global]) do
+      [unique: strip_source(index, opts[:source])]
+    else
+      _ -> []
+    end
+  end
+
+  def to_constraints(%MyXQL.Error{mysql: %{name: name}, message: message}, _opts)
+      when name in [:ER_ROW_IS_REFERENCED_2, :ER_NO_REFERENCED_ROW_2] do
+    with [_, quoted] <- :binary.split(message, [" CONSTRAINT ", " FOREIGN KEY "]),
+         [_, index | _] <- :binary.split(quoted, @quotes, [:global]) do
+      [foreign_key: index]
+    else
+      _ -> []
+    end
+  end
+
+  def to_constraints(
+        %MyXQL.Error{mysql: %{name: :ER_CHECK_CONSTRAINT_VIOLATED}, message: message},
+        _opts
+      ) do
+    with [_, quoted] <- :binary.split(message, ["Check constraint "]),
+         [_, constraint | _] <- :binary.split(quoted, @quotes, [:global]) do
+      [check: constraint]
+    else
+      _ -> []
+    end
+  end
+
+  def to_constraints(_, _),
+    do: []
+
+  defp strip_source(name, nil), do: name
+  defp strip_source(name, source), do: String.trim_leading(name, "#{source}.")
+end