How Can We Efficiently Convert Entities to DTOs in EF Core, Including Single-Entity Child Properties?

Use reusable code for custom DTO transformations in EF Core: single entity subproperty

Problem Statement:

How to extend entity to DTO object conversion to include non-collection sub-properties when querying data using Entity Framework Core?

Implementation:

In EF Core, expressions are used to convert entities to DTOs, which works great for main entities and their subcollections. However, applying this approach to non-collective subproperties has proven challenging.

Solution:

To solve this problem, we can make use of libraries such as LINQKit, NeinLinq or DelegateDecompiler. These libraries allow us to define a transformation function that contains a main entity and additional child properties.

Example:

Using LINQKit:

[Expandable(nameof(AsDtoImpl))]
public static ModelDto AsDto(Model model)
{
   _asDtoImpl ??= AsDtoImpl().Compile();
   return _asDtoImpl(model);
}

private static Func<Model, ModelDto> _asDtoImpl;

private static Expression<Func<Model, ModelDto>> AsDtoImpl =>
    model => new ModelDto
    { 
        ModelId = model.ModelId,
        ModelName = model.ModelName,
        ChildModels = model.ChildModels.AsQueryable().Select(ChildModel.AsDto).ToList(),
        AnotherChildModel = new AnotherChildModelDto
        {
            AnotherChildModelId = model.AnotherChildModel.AnotherChildModelId //修正此处
        }
    };

Queries can be expanded before execution using the library's AsExpandable() function:

dbContext.Models
   .Where(m => SomeCriteria)
   .Select(m => Model.AsDto(m))
   .AsExpandable()
   .ToList();

For LINQKit, this process can be simplified by enabling expression expansion globally in the DbContext configuration. Other libraries such as NeinLinq and DelegateDecompiler provide similar methods. Note that the way the AnotherChildModel attribute is accessed in the sample code has been modified to more accurately reflect the process of getting a model.AnotherChildModel from a AnotherChildModelId. This assumes that AnotherChildModel is an object and not a separate ID.

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