在 Include 中使用的 Lambda 表达式在 Entity Framework Core 中无效

Question

I want to do query in EntityFramework Core 3.1

This is my query:

return await context_client.Tbcategoriapregunta.Include(e => e.Tbpreguntasfrecuentes.Where(preguntas => preguntas.Dstipousuario == user)).ToListAsync();

But not works, this the message error

Lambda expression used inside Include is not valid.

This is de message StackTrace

at Microsoft.EntityFrameworkCore.Query.Internal.NavigationExpandingExpressionVisitor.ProcessInclude(NavigationExpansionExpression source, Expression expression, Boolean thenInclude) at Microsoft.EntityFrameworkCore.Query.Internal.NavigationExpandingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression) at System.Linq.Expressions.MethodCallExpression.Accept(ExpressionVisitor visitor) at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node) at Microsoft.EntityFrameworkCore.Query.Internal.NavigationExpandingExpressionVisitor.Expand(Expression query) at Microsoft.EntityFrameworkCore.Query.QueryTranslationPreprocessor.Process(Expression query) at Microsoft.EntityFrameworkCore.Query.QueryCompilationContext.CreateQueryExecutor[TResult](Expression query) at Microsoft.EntityFrameworkCore.Storage.Database.CompileQuery[TResult](Expression query, Z27226C864BAC7454A8504F8EDB15D95B Z async) at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.CompileQueryCore[TResult](IDatabase database, Expression query, IModel model, Boolean async) at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass12_0 1.<ExecuteAsync>b__0() at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQueryCore[TFunc](Object cacheKey, Func 1 compiler) at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQuery[TResult](Object cacheKey, Func 1 compiler) at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.ExecuteAsync[TResult](Expression query, CancellationToken cancellationToken) at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.ExecuteAsync[TResult](Expression expression, CancellationToken cancellationToken) at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable 1.GetAsyncEnumerator(CancellationToken cancellationToken) at Microsoft .EntityFrameworkCore.EntityFrameworkQueryableExtensions.IncludableQueryable 2.GetAsyncEnumerator(CancellationToken cancellationToken) at System.Runtime.CompilerServices.ConfiguredCancelableAsyncEnumerable 1.GetAsyncEnumerator() at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.d__64 1.MoveNext() at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter 1.GetResult() at Business.Implementation.BsCategoriaPregunta.d__4.MoveNext() in C:\Users\admin\source\repos\API013-Ayuda\Business\Implementation\BsCategoriaPregunta.cs:line 58

Any idea...???

Answer 1

The purpose of Include() is to tell it to load data from a related table at the same time that this query is processed.

The example in the documentation uses a scenario where you want to load a list of blogs from the database and also include the posts related to each blog:

using (var context = new BloggingContext())
{
    var blogs = context.Blogs
        .Include(blog => blog.Posts)
        .ToList();
}

So it would not make sense to have a Where() inside Include() .

You will have to tell us what you are trying to do. But maybe something like this might work?

return await context_client.Tbcategoriapregunta
    .Include(e => e.Tbpreguntasfrecuentes)
    .Where(categoria => categoria.Tbpreguntasfrecuentes.Dstipousuario == user)
    .ToListAsync();