Generate UUID primary keys in the database

db/migrations/20180625202051_create_line_item.cr

@@ -1,5 +1,7 @@
 class CreateLineItem::V20180625202051 < Avram::Migrator::Migration::V1
   def migrate
+    enable_extension "pgcrypto"
+
     create :line_items do
       primary_key id : UUID
       add_timestamps

db/migrations/20180628193054_create_product.cr

@@ -4,9 +4,6 @@ class CreateProduct::V20180628193054 < Avram::Migrator::Migration::V1
       primary_key id : UUID
       add_timestamps
     end
-
-    enable_extension "uuid-ossp"
-    execute("ALTER TABLE products ALTER COLUMN id SET DEFAULT uuid_generate_v4();")
   end
 
   def rollback

spec/migrator/create_table_statement_spec.cr

@@ -50,7 +50,7 @@ describe Avram::Migrator::CreateTableStatement do
     built.statements.size.should eq 1
     built.statements.first.should eq <<-SQL
     CREATE TABLE users (
-      id uuid PRIMARY KEY);
+      id uuid PRIMARY KEY DEFAULT gen_random_uuid());
     SQL
 
     built = Avram::Migrator::CreateTableStatement.new(:users).build do

spec/schema_enforcer/ensure_uuid_primary_key_has_default_spec.cr

@@ -6,7 +6,7 @@ private class TableWithoutUUIDPrimaryKey < BaseModel
 end
 
 private class TableWithoutDefaultUUID < BaseModel
-  table :line_items do
+  table :prices do
   end
 end
 
@@ -23,7 +23,7 @@ describe Avram::SchemaEnforcer::EnsureUUIDPrimaryKeyHasDefault do
   end
 
   it "raises when table's uuid primary key does not have default" do
-    expect_schema_mismatch "Primary key on the 'line_items' table has the type set as uuid but does not have a default value." do
+    expect_schema_mismatch "Primary key on the 'prices' table has the type set as uuid but does not have a default value." do
       Avram::SchemaEnforcer::EnsureUUIDPrimaryKeyHasDefault.new(TableWithoutDefaultUUID).validate!
     end
   end

src/avram/migrator/columns/primary_keys/uuid_primary_key.cr

@@ -8,5 +8,9 @@ module Avram::Migrator::Columns::PrimaryKeys
     def column_type : String
       "uuid"
     end
+
+    def build : String
+      %(  #{name} #{column_type} PRIMARY KEY DEFAULT gen_random_uuid())
+    end
   end
 end