I would like to use AutoMapper for mapping a EntityDto with nested List to the Entity, then update it with a SaveChanges() call.

The problem is that AutoMapper maps nested List elements as new objects, so EntityFramework thinks I want to add new objects with already existing Ids.

Example:

    public class Entity
    {
        public Guid Id { get; set; }
        public List<NestedEntity> NestedEntityList { get; set; }
    }

    public class EntityDto
    {
        public Guid Id { get; set; }
        public List<NestedEntityDto> NestedEntityList { get; set; }
    }

    public class NestedEntity
    {
        public Guid Id { get; set; }
        public string PropertyOne { get; set; }
        public string PropertyTwo { get; set; }
    }

    public class NestedEntityDto
    {
        public Guid Id { get; set; }
        public string PropertyTwo { get; set; }
    }

Entity has for example a list that contains 2 NestedEntity objects

{
    "Id": "EntityId"
    "NestedEntityList": [
        {
            "Id": "A",
            "PropertyOne": "Value A",
            "PropertyTwo": "Value AA"
        },
        {
            "Id": "B",
            "PropertyOne": "Value B",
            "PropertyTwo": "Value BB"
        }
    ]
}

Update: (A modified, B deleted, C added)

EntityDto has a list that contains 2 NestedEntity objects

{
    "Id": "EntityId"
    "NestedEntityList": [
        {
            "Id": "A",
            "PropertyTwo": "Value AAA (Updated)"
        },
        {
            "Id": "C",
            "PropertyTwo": "Value CC"
        }
    ]
}

Without further configuration AutoMapper maps NestedEntityList by creating new objects. This results in 2 problems:

1. EntityFramework will track these new objects as freshly created objects instead of existing objects that were updated. This results in the following error message: "The instance of entity type "NestedEntity" cannot be tracked because another instance with the key value "A" is already being tracked".
2. If NestedEntity has a PropertyOne value, then after the mapping, it will be null, because NestedEntityDto does not have PropertyOne. I want to update the properties in the EntityDto (which is PropertyTwo) and keep the value of everything else.

So the result that I would like to achieve: (A modified, B deleted, C added)

{
    "Id": "EntityId"
    "NestedEntityList": [
        {
            "Id": "A",
            "PropertyOne": "Value A", //Old value, not updated with NULL
            "PropertyTwo": "Value AAA (Updated)" //Updated value
        },
        {
            "Id": "C", //New item added in the update
            "PropertyOne": NULL,
            "PropertyTwo": "Value CC"
        }
    ]
}

How do I need to configure AutoMapper to achieve this? Is it possible at all?

CodePudding user response：

When mapping to an existing collection, the destination collection is cleared first. If this is not what you want, take a look at AutoMapper.Collection.