Implement lock feature

spec/adapters/mysql_adapter_spec.cr

@@ -114,5 +114,20 @@ if Repo.config.adapter == Crecto::Adapters::Mysql
         sql.should eq(["SELECT posts.* FROM posts INNER JOIN users ON users.id = posts.user_id"])
       end
     end
+
+    it "should generate sql for query syntax with lock" do
+      query = Query
+        .where(name: "fridge")
+        .where("users.things < ?", [124])
+        .order_by("users.name ASC")
+        .order_by("users.things DESC")
+        .limit(1)
+      Repo.config.get_connection.transaction do |tx|
+        Repo.lock(tx, User, query)
+      end
+      check_sql do |sql|
+        sql.should eq(["SELECT users.* FROM users WHERE  (users.name=?) AND (users.things < ?) ORDER BY users.name ASC, users.things DESC LIMIT 1 FOR UPDATE"])
+      end
+    end
   end
 end

spec/adapters/postgres_adapter_spec.cr

@@ -103,5 +103,20 @@ if Repo.config.adapter == Crecto::Adapters::Postgres
         sql.should eq(["SELECT posts.* FROM posts INNER JOIN users ON users.id = posts.user_id"])
       end
     end
+
+    it "should generate sql for query syntax with lock" do
+      query = Query
+        .where(name: "fridge")
+        .where("users.things < ?", [124])
+        .order_by("users.name ASC")
+        .order_by("users.things DESC")
+        .limit(1)
+      Repo.config.get_connection.transaction do |tx|
+        Repo.lock(tx, User, query)
+      end
+      check_sql do |sql|
+        sql.should eq(["SELECT users.* FROM users WHERE  (users.name=$1) AND (users.things < $2) ORDER BY users.name ASC, users.things DESC LIMIT 1 FOR UPDATE"])
+      end
+    end
   end
 end

spec/repo_spec.cr

@@ -1301,6 +1301,34 @@ describe Crecto do
       end
     end
 
+    describe "#lock" do
+      it "should return rows" do
+        unless Repo.config.adapter == Crecto::Adapters::SQLite3
+          users = [] of User
+          Repo.config.get_connection.transaction do |tx|
+            users = Repo.lock(tx, User)
+          end
+          users.size.should be > 0
+        end
+      end
+
+      it "should return rows with Query" do
+        unless Repo.config.adapter == Crecto::Adapters::SQLite3
+          query = Query
+            .where(name: "fridge")
+            .where("users.things < ?", [124])
+            .order_by("users.name ASC")
+            .order_by("users.things DESC")
+            .limit(1)
+          users = [] of User
+          Repo.config.get_connection.transaction do |tx|
+            users = Repo.lock(tx, User, query)
+          end
+          users.size.should be > 0
+        end
+      end
+    end
+
     # keep this at the end
     describe "#delete_all" do
       it "should delete destroy dependents" do

src/crecto/adapters/base_adapter.cr

@@ -13,6 +13,8 @@ module Crecto
           all(conn, queryable, query)
         when :delete_all
           delete(conn, queryable, query)
+        when :lock
+          all(conn, queryable, query, true)
         end
       end
 
@@ -153,8 +155,7 @@ module Crecto
         builder << " SELECT " << ag << '(' << queryable.table_name << '.' << field << ") FROM " << queryable.table_name
       end
 
-
-      private def all(conn, queryable, query)
+      private def all(conn, queryable, query, for_update = false)
         params = [] of DbValue | Array(DbValue)
 
         q = String.build do |builder|
@@ -177,6 +178,7 @@ module Crecto
           limit(builder, query)
           offset(builder, query)
           group_by(builder, query)
+          builder << " FOR UPDATE" if for_update
         end
 
         execute(conn, position_args(q), params)

src/crecto/live_transaction.cr

@@ -26,5 +26,9 @@ module Crecto
     def update_all(queryable, query, update_tuple : NamedTuple)
       update_all(queryable, query, update_tuple.to_h)
     end
+
+    def lock(queryable, query = Crecto::Repo::Query.new)
+      @repo.lock(@tx, queryable, query)
+    end
   end
 end

src/crecto/repo.cr

@@ -533,6 +533,20 @@ module Crecto
       end
     end
 
+    # Returns a list of locked *queryable* instances.  Accepts an optional `query`
+    #
+    # ```
+    # Crecto::Repo.config.get_connection.transaction do |tx|
+    #   users = Crecto::Repo.lock(tx, User)
+    # end
+    # ```
+    def lock(tx : DB::Transaction, queryable, query = Query.new) : Array
+      raise Crecto::InvalidAdapter.new "SQLite3 cannot use lock feature." if config.adapter == Crecto::Adapters::SQLite3
+      q = config.adapter.run(tx, :lock, queryable, query).as(DB::ResultSet)
+      results = queryable.from_rs(q)
+      results
+    end
+
     {% for operation in %w[insert update delete] %}
       private def run_operation(operation : Multi::{{operation.camelcase.id}}, tx)
         {{operation.id}}(operation.instance, tx)