public TableCreateUnitTest()
        {
            // create table 命令构建.
            categoriesBuilder = new DbCommandBuilder();
            categoriesBuilder.CreateTable(table_categories).ColumnsDefine(
                DbTableColumnDefinition.New(name: "Id", dataType: GenericDbType.Int, notNull: true, identity: new DbColumnIdentity(0, 1), pk: true),
                DbTableColumnDefinition.New(name: "CategoryName", dataType: GenericDbType.VarChar, size: 255, notNull: true, unique: true),
                DbTableColumnDefinition.New(name: "Remark", dataType: GenericDbType.VarChar, size: 300),
                DbTableColumnDefinition.New(name: "Cover", dataType: GenericDbType.Image),
                DbTableColumnDefinition.New(name: "CreationDate", dataType: GenericDbType.DateTime, notNull: true, Default: Fun.Now())
                );

            productsBuilder = new DbCommandBuilder();
            productsBuilder.CreateTable(table_products).ColumnsDefine(
                DbTableColumnDefinition.New(name: "Id", dataType: GenericDbType.Int, notNull: true, identity: new DbColumnIdentity(0, 1), pk: true),
                DbTableColumnDefinition.New(name: "Category", dataType: GenericDbType.Int, notNull: true, fk: new DbForeignKey(table_categories, "Id")),
                DbTableColumnDefinition.New(name: "Name", dataType: GenericDbType.VarChar, size: 32, notNull: true, unique: true),
                DbTableColumnDefinition.New(name: "Price", dataType: GenericDbType.Single, Default: 0f),
                DbTableColumnDefinition.New(name: "Quantity", dataType: GenericDbType.SmallInt, Default: 0),
                DbTableColumnDefinition.New(name: "Remark", dataType: GenericDbType.VarChar, size: 300),
                DbTableColumnDefinition.New(name: "TimeOf", dataType: GenericDbType.DateTime, Default: Fun.Now()),
                DbTableColumnDefinition.New(name: "Picture", dataType: GenericDbType.Image)
                );
        }