Entity Framework Include Filters

The location where you filter (included) entities is important, as it has a significant impact on the result set. Without knowing the details, it's easy to make assumptions and make a subtle mistake while filtering entities.

I know I made the mistake numerous times, even not so long ago, and I'm sure I'm not the only one. That's why I decided to write this Bit, to raise awareness about the small but important details.

The following examples illustrate the difference between including filtered entities (using Where), and filtering entities after the include (using Any in this example) statement.

 content_paste
[
  {
    "FullName": "Tiffany Gerlach",
    "Addresses": [
      {
        "Street": "70 Delmer Ways",
        "ZipCode": "2377"
      },
      {
        "Street": "61 Trisha River",
        "ZipCode": "7470"
      }
    ]
  },
  {
    "FullName": "Milford Nader",
    "Addresses": [
      {
        "Street": "86 Feeney Pine",
        "ZipCode": "6560"
      },
      {
        "Street": "23 Hauck Run",
        "ZipCode": "3610"
      }
    ]
  }
]

The first example retrieves all persons and only includes the addresses matching the ZipCode predicate. Does not filter the "root" entity.

 content_paste
var persons = await dbContext.Set<Person>()
  .Include(p => p.Addresses.Where(a => a.ZipCode == "7470"))
  .ToListAsync();

 content_paste
[
  {
    "FullName": "iffany Gerlach",
    "Addresses": [
      {
        "Street": "61 Trisha River",
        "ZipCode": "7470"
      }
    ]
  },
  {
    "FullName": "Milford Nader",
    "Addresses": []
  }
]

The second example only retrieves persons that contain the specified ZipCode condition, with all their addresses. Filters the "root" entity, not the children.

 content_paste
var persons = await dbContext.Set<Person>()
  .Include(p => p.Addresses)
  .Where(p => p.Addresses.Any(a => a.ZipCode == "7470"))
  .ToListAsync();

 content_paste
[
  {
    "FullName": "Tiffany Gerlach",
    "Addresses": [
      {
        "Street": "70 Delmer Ways",
        "ZipCode": "2377"
      },
      {
        "Street": "61 Trisha River",
        "ZipCode": "7470"
      }
    ]
  }
]

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