C# Linq find particular item in nested array object

Question

I am developing an application using asp.net core webapi and azure cosmosdb. I need to find an item from the list of objects. I am not experienced with linq. In the below json, i need to find a sector id who got a learnerId": "123". I am expecting output like:

"id": "7d65fa4c-86ed-4e07-9e9a-a1583df5715c"

Sector:

[
  {
    "name": "Emp1",
    "edsNumber": "",
    "sectors": [
      {
        "id": "7d65fa4c-86ed-4e07-9e9a-a1583df5715c",
        "name": "Technology1",
        "learners": [
          {
            "learnerId": "123",
            "learnerName": "Learner1",
            "dateAdded": 1612872051
          },
          {
            "learnerId": "456",
            "learnerName": "Learner2",
            "dateAdded": 1612877369
          },
          {
            "learnerId": "789",
            "learnerName": "Learner3",
            "dateAdded": 1612877372
          },
          {
            "learnerId": "12314",
            "learnerName": "Learner4",
            "dateAdded": 1613065233
          },
          {
            "learnerId": "2346",
            "learnerName": "Learner5",
            "dateAdded": 1613577350
          }
        ],
        "course": {
          "name": "Angularv10",
          "isCompleted": true
        },
        "contact": {
          "name": "Voytek",
          "jobTitle": "Designer1",
          "email": "[email protected]",
          "isCompleted": true
        }
      }
    ]
  },
  {
    "name": "Emp2",
    "edsNumber": "",
    "sectors": [
      {
        "id": "7d65fa4c-86ed-4e07-9e9a-a1583df5235c",
        "name": "Technology1",
        "learners": [
          {
            "learnerId": "834457",
            "learnerName": "Learner6",
            "dateAdded": 1612872051
          },
          {
            "learnerId": "11122",
            "learnerName": "Learner7",
            "dateAdded": 1612877369
          }
        ],
        "course": {
          "name": "Angularv10",
          "isCompleted": true
        },
        "contact": {
          "name": "Voytek",
          "jobTitle": "Designer1",
          "email": "[email protected]",
          "isCompleted": true
        }
      }
    ]
  }
]

I tried the following:

        var sectorId = (from e in employers
                      from s in e.Sectors
                      from l in s.Learners
                      where l.LearnerId == learnerEntity.Id
                      select s.Id).FirstOrDefault();

Is there a better way to achieve? And how to get both the SectorId and the employer the sector belongs to?

Sergey Kalinichenko · Accepted Answer · 2021-02-20 12:36:35Z

7

LINQ query that looks for a single item that satisfies a condition on a child object would have two components:

A call to SingleOrDefault (or Single if the item you look for must be there), and
A call to Any nested inside the first condition to see that the child item is there.

Since your sectors are embedded inside employers, you could flatten the list with SelectMany.

Here is how it would look:

var sectorId = employers
    .SelectMany(e => e.Sectors) // Flatten sectors
    .SingleOrDefault(
        s => s.Learners.Any(sl => sl.Id == targetId)
    ).Id;

answered Feb 20, 2021 at 12:36

Sergey Kalinichenko

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3 Comments

Igor Meszaros Over a year ago

Due to the inexperience of the poster I would like to add on that SingleOrDefault will throw an exception of more than 1 element is found.

Mukil Deepthi Over a year ago

@Sergey Thanks for your reply. Along with the sectorId i need the employer name to which the sectorid belongs? Can you please help me get this as well? Thanks

Sergey Kalinichenko Over a year ago

@MukilDeepthi If you'd like to get the employer as well, use the trick with Any(...) two times -

var employer = employers.SingleOrDefault(e => e.Sectors.Any(s => s.Learners.Any(...)). Once you have the employer, run the second query on the

employer.Sectors` to get the sector.

Poilaupat · Accepted Answer · 2021-02-20 13:10:45Z

0

This is not very clear in the question, but "sectors" is obviously an array. If an employee has more than one sector and the searched LearnerId is expected to appear in two or more sectors, then, returning an enumeration of sectorId will be necessary :

(Slithly different version based on Sergey Kalinichenko answer):

IEnumerable<Guid> sectorIds = employers
.SelectMany(e => e.Sectors) // Flatten sectors
.Where(s => s.Learners.Any(sl => sl.Id == targetId))
.Select(s => s.Id);

answered Feb 20, 2021 at 13:10

Poilaupat

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