Creating a rights hierarchy in a graph structure

[slava]

Welcome to the community, @Marcus_Lindner!

@Marcus_Lindner

{
    "_id" : NumberLong(3),
    "name" : "Mauer",
    "rights" : [ 
        {
            "to" : NumberLong(1),
            "type" : "write",
            "level" : NumberLong(0)
        }, 
        {
            "to" : NumberLong(2),
            "type" : "read",
            "level" : NumberLong(1)
        }
    ]
}

I get the link to the document with _id 2 but the link to document with the _id 1 is ignored.

This can be achieved with this aggregation pipeline:

db.test1.aggregate([
  {
    // match the users, that you want to
    // join permissions on other users
    // (this stage can be omitted or modified as desired)
    $match: {
      name: 'Mauer'
    }
  },
  {
    // unwind the 'rights' array,
    // so it would be possible to join only the users,
    // that a given user has enough rights
    $unwind: '$rights',
  },
  {
    // filter the users to join here;
    // feel free to change the matching params
    $match: {
      'rights.type': 'read',
      'rights.level': {
        $gte: 1,
      }
    }
  },
  {
    $group: {
      _id: '$_id',
      name: {
        $first: '$name',
      },
      rights: {
        $push: '$rights',
      }
    }
  },
  {
    $graphLookup: {
      from: 'test1',
      startWith: '$rights.to',
      connectFromField: 'rights.to',
      // set maxDepth to 0, so
      // dependencies of the dependencies
      // would not join
      maxDepth: 0,
      connectToField: '_id',
      as: 'hasRequiredRightsOn',
    }
  },
  {
    // (optionally)
    // clean-up
    $project: {
      rights: false,
      'hasRequiredRightsOn.rights': false,
    }
  }
]).pretty();

Tested on the below dataset. I have prettified and reformatted it slightly, so it would be more readable and work in the mongo-shell. The data is kept untouched, though.

db.test1.insertMany([
  {
    _id: 1,
    name: "Hugo",
    rights: []
  },
  {
    _id: 2,
    name: "Hermann",
    rights: [
      { to: 1, type: "write", level: 0 }
    ]
  },
  {
    _id: 3,
    name: "Mauer",
    rights: [
      { to: 1, type: "write", level: 0 },
      { to: 2, type: "read", level: 1 }
    ]
  },
  {
    _id: 4,
    name: "Jon",
    rights: [
      { to: 1, type: "read", level: 1 },
      { to: 2, type: "read", level: 1 }
    ]
  },
  {
    _id: 5,
    name: "Jane",
    rights: [
      { to: 1, type: "write", level: 0 },
      { to: 3, type: "write", level: 0 },
      { to: 6, type: "read", level: 1 },
      { to: 4, type: "read", level: 1 }
    ]
  },
  {
    _id: 6,
    name: "Michael",
    rights: [
      { to: 4, type: "read", level: 1 },
      { to: 5, type: "read", level: 1 }
    ]
  }
]);

The output of the above aggregation will look like this (notice, that only required users are joined):

{
  "_id" : 3,
  "name" : "Mauer",
  "hasRequiredRightsOn" : [
    {
      "_id" : 2,
      "name" : "Hermann"
    }
  ]
}

You can include additional fields into the output with the $project stage.