The type or namespace name 'RequiredAttribute' could not be found (are you missing a using directive or an assembly reference?)

The type or namespace name 'Required' could not be found (are you missing a using directive or an assembly reference?)

The type or namespace name 'DataTypeAttribute' could not be found (are you missing a using directive or an assembly reference?)

The type or namespace name 'DataType' could not be found (are you missing a using directive or an assembly reference?)

The type or namespace name 'StringLengthAttribute' could not be found (are you missing a using directive or an assembly reference?)

The type or namespace name 'StringLength' could not be found (are you missing a using directive or an assembly reference?)

The name 'DataType' does not exist in the current context

The type or namespace name 'RequiredAttribute' could not be found (are you missing a using directive or an assembly reference?)

The type or namespace name 'Required' could not be found (are you missing a using directive or an assembly reference?)