Allow using cascade when truncating tables

db/migrations/20210710000000_add_constraint_comments.cr

@@ -0,0 +1,17 @@
+class AddConstraintComments::V20210710000000 < Avram::Migrator::Migration::V1
+  def migrate
+    execute <<-SQL
+      ALTER TABLE comments
+        ADD CONSTRAINT fk_columns_has_post
+        FOREIGN KEY (post_id)
+        REFERENCES posts (custom_id);
+    SQL
+  end
+
+  def rollback
+    execute <<-SQL
+      ALTER TABLE comments
+      DROP CONSTRAINT fk_columns_has_post;
+    SQL
+  end
+end

spec/queryable_spec.cr

@@ -26,6 +26,12 @@ class QueryWithDefault < User::BaseQuery
   end
 end
 
+class CommentQuery < Comment::BaseQuery
+end
+
+class PostQuery < Post::BaseQuery
+end
+
 describe Avram::Queryable do
   it "can chain scope methods" do
     ChainedQuery.new.young.named("Paul")
@@ -1073,9 +1079,24 @@ describe Avram::Queryable do
     it "truncates the table" do
       10.times { UserFactory.create }
       UserQuery.new.select_count.should eq 10
+      # NOTE: we don't test rows_affected here because this isn't
+      # available with a truncate statement
       UserQuery.truncate
       UserQuery.new.select_count.should eq 0
     end
+
+    it "deletes associated data when cascade is true" do
+      post_with_matching_comment = PostFactory.create
+      comment = CommentFactory.new
+        .post_id(post_with_matching_comment.id)
+        .create
+
+      PostQuery.truncate cascade: true
+      PostQuery.new.select_count.should eq 0
+      expect_raises(Avram::RecordNotFoundError) do
+        CommentQuery.new.find(comment.id)
+      end
+    end
   end
 
   describe "#update" do

src/avram/queryable.cr

@@ -44,9 +44,19 @@ module Avram::Queryable(T)
       new.none?
     end
 
-    def self.truncate
+    # Removes all data from a table using the TRUNCATE postgres SQL command.
+    #
+    # You should run this command with `cascade: true` if your table
+    # columns are referenced by other foreign key constraints. Use *delete*
+    # instead if you don't want to accidentally delete rows referenced
+    # elsewhere.
+    #
+    # To delete all data referenced by foreign keys as well, set *cascade*
+    # to true.
+    def self.truncate(*, cascade : Bool = false)
       query = self.new
-      query.database.exec "TRUNCATE TABLE #{query.table_name}"
+      cascade_str = cascade ? " CASCADE" : ""
+      query.database.exec "TRUNCATE TABLE #{query.table_name}#{cascade_str}"
     end
   end