域驱动设计，映射器/存储库值高于/低于

Question

In a project I am working on we use domain driven design. With this we also use the mapper and repository pattern. Where the mapper are just the crud action, and the repository are look like the entity.

So it looks like something like

class UserMapper
{
    public function fetch($criteria)
    {
         // magic on the database
    }
}

class UserRepository
{
    public function getByName($name)
    {
        $this->mapper->fetch(array('name' =>  $name));
    }
}

Code will not work, but it gives a general idea

Now I come with the following problem

Let's say I want the user with the name "john" and with gender "male". Should the Repository now have a function getByNameAndGender($name, $gender). But then you would get soon a lot of functions because you need where gender, age and name etc.

Next is that all the examples i find only implement the following "value == value". But not a single example was found with fomething like "value < value" or something else. So my question is how do you implement this. Because again I can see that you could make functions like

getWhereHeightIsLowerThan($height)
getWhereHeightIsLowerThanOrEquals($height)
getWhereHeightIs($height)
getWhereHeightIsGreaterThan($height)
getWhereHeightIsGreaterThanOrEquals($height)

Again 5 functions for something that should be like 1 function. How do you implement this in the repository / mapper pattern. To make things even more complecated, I am not using a SQL database. But MongoDB, now that shouldn't be a big issue.

--

Using the answer given by eulerfx i came with with following code

use Application\\Specification\\AbstractSpecification;

class IdIsSpecification extends AbstractSpecification
{
    /** @var  string */
    protected $id;

    /**
     * @param $id
     * @throws \InvalidArgumentException
     */
    function __construct($id)
    {
        if(!is_string($id))
        {
            throw new \InvalidArgumentException('Expects string, given ' . gettype($id));
        }

        $this->id = $id;
    }

    /**
     * @return mixed
     */
    public function getQuery()
    {
        return [
            '_id' => new \MongoId($this->id),
        ];
    }
}

I use php and so I can't use the words AND and OR so renamed them to ALSO and OF.

Also the specification patterns look over a dataset that is throw at it. This is for my needs not the best way, so I have the method getQuery instead of isSatisfied.

All the query logic is found in the specification. The repository builds up with the specification comon functions, like get by id.

And the mapper is just the simple crud handler of the datase (fetch, fetchAll, count, insert, etc).

At the end I only have to change the getQuery methods if I want to change the database language (from mongo syntax to sql). Hope it helps some one

Answer 1

It seems that you're trying to address the complexity in complex queries. For this, you can use the specification pattern . With the specification pattern, you'd have an object representing the query. This object would be composed of predicates about the entity at hand, such as WhereHeightIsLowerThan 3 . The repository would then build a SQL query or a MongoDB query based on this specification object.