Pomelo.entityframeworkcore.mysql: InvalidOperationException: Calling ShapedQueryExpression.VisitChildren is not allowed. Visit expression manually for relevant part.

[esdrasdemorais]

Steps to reproduce

context.Set<T>().ToList();

The issue

The GetAll() Generic Repository Method doesn't work.

Exception message:
An unhandled exception occurred while processing the request.
InvalidOperationException: Calling ShapedQueryExpression.VisitChildren is not allowed. Visit expression manually for relevant part.
Microsoft.EntityFrameworkCore.Query.ShapedQueryExpression.VisitChildren(ExpressionVisitor visitor)



Stack trace:
Microsoft.EntityFrameworkCore.Query.ShapedQueryExpression.VisitChildren(ExpressionVisitor visitor)
Pomelo.EntityFrameworkCore.MySql.Query.ExpressionVisitors.Internal.MySqlCompatibilityExpressionVisitor.VisitExtension(Expression extensionExpression)
Pomelo.EntityFrameworkCore.MySql.Query.ExpressionVisitors.Internal.MySqlQueryTranslationPostprocessor.Process(Expression query)
Microsoft.EntityFrameworkCore.Query.QueryCompilationContext.CreateQueryExecutor<TResult>(Expression query)
Microsoft.EntityFrameworkCore.Storage.Database.CompileQuery<TResult>(Expression query, bool async)
Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.CompileQueryCore<TResult>(IDatabase database, Expression query, IModel model, bool async)
Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler+<>c__DisplayClass12_0<TResult>.<ExecuteAsync>b__0()
Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQueryCore<TFunc>(object cacheKey, Func<Func<QueryContext, TFunc>> compiler)
Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQuery<TResult>(object cacheKey, Func<Func<QueryContext, TResult>> compiler)
Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.ExecuteAsync<TResult>(Expression query, CancellationToken cancellationToken)
Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.ExecuteAsync<TResult>(Expression expression, CancellationToken cancellationToken)
Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable<TResult>.GetAsyncEnumerator(CancellationToken cancellationToken)
Microsoft.AspNetCore.Mvc.Infrastructure.AsyncEnumerableReader.ReadInternal<T>(object value)
Microsoft.AspNetCore.Mvc.Infrastructure.ObjectResultExecutor.ExecuteAsyncEnumerable(ActionContext context, ObjectResult result, object asyncEnumerable, Func<object, Task<ICollection>> reader)
Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResultFilterAsync>g__Awaited|29_0<TFilter, TFilterAsync>(ResourceInvoker invoker, Task lastTask, State next, Scope scope, object state, bool isCompleted)
Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResultExecutedContextSealed context)
Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.ResultNext<TFilter, TFilterAsync>(ref State next, ref Scope scope, ref object state, ref bool isCompleted)
Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeResultFilters()
Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|19_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, object state, bool isCompleted)
Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

Further technical details

MySQL version: 10.4.12-MariaDB
Operating system: Linux 64 bits
Pomelo.EntityFrameworkCore.MySql version: 3.1.1
Microsoft.AspNetCore.App version: 3.1.201

Other details about my project setup:
Entity Framework 3.1.3

[lauxjpn]

What is the full LINQ query you are running? What is the actual type that is being used for T?

[esdrasdemorais]

Just a call: context.Set().AsEnumerable(), T is a Simple Object with a ICollection Property.

But in fact, Looking with more attention I noted that Microsoft.EntityFrameworkCore.Tools and Microsoft.EntityFrameworkCore.Design are in 5.0 preview version.

[lauxjpn]

Please post the actual LINQ query (the real one), the model classes of all entities involved in the query and the model definitions (FluentAPI) of the models involved.

[esdrasdemorais]

Repository Method:

public IEnumerable<T> Get()
{
    var collection = context.Set<T>().AsEnumerable<T>();
    return collection.ToList();
}

LINQ query (the line when throw the Exception):

context.Set<Maintenance>().AsEnumerable<Maintenance>();

Model Classes:
```
public class Maintenance {
public Int32 Id { get; set; }
private Int32 maxLengthPerLine = 380;
public Int32 MaxLengthPerLine {
get { return maxLengthPerLine; }
set { maxLengthPerLine = value; }
}
public DateTime CreatedDate { get; set; }
public IEnumerable Registers { get; set; }
public Boolean IsGeneratedFile { get; private set; }
public DateTime? GeneratedDate { get; set; }
public Boolean IsRejectedFile { get; private set; }
public DateTime? RejectedDate { get; set; }

    public String DataOldJson { get; set; }

}

public abstract class IRegister {
public Int32 Id { get; set; }

    public Int32 MaintenanceFileLayoutId { get; set; }

    protected Type type;
    public Type GetType {
        get { return type; }
        set { type = value; }
    }

    public DateTime CreatedDate { get; set; }

}

[lauxjpn]

The following is not going to work:

```c#
public IEnumerable Registers { get; set; }

Firstly, it isn't going to work, because your `IRegister` entity defines the following public property:

```c#
public Type GetType {
    get { return type; }
    set { type = value; }
}

Since you don't ignore the property (at least you did not provide any FluentAPI model definition for it, so I have to assume, that there is none), EF Core will try to map the Type CLR type to a database store type, which it will not be able to.

You could however save a string with the type's name if that is enough for you. So instead of using your custom GetType, use something like the following instead:

```c#
[NotMapped]
public Type Type { get; set; }

public string TypeName
{
get => Type.FullName;
set => Type = Type.GetType(value);
}

You can then use the `Type` property in your app and use the `TypeName` property for database persistency.

---

Couple of side notes:

Because every object has a `GetType()` method and you are using a property with the same name here, you either want to change the name of your custom property, or use the `new` keyword (`public new Type GetType {}`). If you use my suggestion from above, this is of course not necessary, because this property does not exist anymore.

The `Get<T>` method of your repository does not need to call `AsEnumerable<T>()`, because it is using `.ToList()` anyway in the next line, which materializes the query as well. But then you return an `IEnumerable<T>` again, which does not make sense.

So either use this:

```c#
public IEnumerable<T> Get<T>()
    where T : class
    => Set<T>().AsEnumerable();

Or this:

c# public List<T> Get<T>() // or IList<T> where T : class => Set<T>().ToList();

Generally, I don't see any advantage to use an explicit repository pattern here at all. DbContext is already a unit-of-work pattern implementation and DbSet is already a repository pattern implementation. So if you don't have a good reason to put another facade around DbSet, you might want to consider using DbSet directly.