When called from 'VisitLambda', rewriting a node of type 'System.Linq.Expressions.ParameterExpression' must return a non-null value of the same type

Question

I upgraded my data layer classlibrary project from .NETCore 2.2 to .NETCore3.1 and also upgraded the Nuget packages like EntityFrameWork Core from 2.2.0 to EFCore 3.1.0.

I then on validating the following code got an error as mentioned below:

Code:

private async Task<List<CountryDTO>> GetCountriesDataAsync(int languageId)
{
    int pageNo = 1, pageSize = 100;
    var images = await _cacheService.GetAllAsync("imagesCacheKey");
    return await _dbContext.Countries
                    .Where(cc => cc.IsPublished.Equals(true) 
                                     && cc.LanguageId.Equals(languageId))
                    .Select(co => new CountryDTO
                            {  Uuid = co.CountryId, 
                               PNGImagePath = images.FirstOrDefault(im => im.ImageId.Equals(co.PNGImageId))
                                                    .FilePath, 
                                SVGImagePath = images.FirstOrDefault(im => im.ImageId.Equals(co.SVGImageId))
                                                    .FilePath, 
                          DisplayName = co.DisplayName, 
                          DisplayNameShort = co.DisplayName, 
                          Name = Helper.ReplaceChars(co.DisplayName), 
                          Path = Helper.ReplaceChars(co.DisplayName), 
                          CompleteResponse = true})
                   .Skip((pageNo - 1) * 100)
                   .Take(pageSize)
                   .ToListAsync();
}

Error:

When called from 'VisitLambda', rewriting a node of type 'System.Linq.Expressions.ParameterExpression' must return a non-null value of the same type. Alternatively, override 'VisitLambda' and change it to not visit children of this type.
 ---> System.InvalidOperationException: When called from 'VisitLambda', rewriting a node of type 'System.Linq.Expressions.ParameterExpression' must return a non-null value of the same type. Alternatively, override 'VisitLambda' and change it to not visit children of this type.
   at System.Linq.Expressions.ExpressionVisitor.VisitAndConvert[T](T node, String callerName)
   at System.Dynamic.Utils.ExpressionVisitorUtils.VisitParameters(ExpressionVisitor visitor, IParameterProvider nodes, String callerName)
   at System.Linq.Expressions.ExpressionVisitor.VisitLambda[T](Expression`1 node)
   at Microsoft.EntityFrameworkCore.Cosmos.Query.Internal.CosmosProjectionBindingExpressionVisitor.Visit(Expression expression)
   at System.Dynamic.Utils.ExpressionVisitorUtils.VisitArguments(ExpressionVisitor visitor, IArgumentProvider nodes)
   at System.Linq.Expressions.ExpressionVisitor.VisitMethodCall(MethodCallExpression node)
   at Microsoft.EntityFrameworkCore.Cosmos.Query.Internal.CosmosProjectionBindingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at Microsoft.EntityFrameworkCore.Cosmos.Query.Internal.CosmosProjectionBindingExpressionVisitor.Visit(Expression expression)
   at Microsoft.EntityFrameworkCore.Cosmos.Query.Internal.CosmosProjectionBindingExpressionVisitor.VisitMember(MemberExpression memberExpression)
   at Microsoft.EntityFrameworkCore.Cosmos.Query.Internal.CosmosProjectionBindingExpressionVisitor.Visit(Expression expression)
   at Microsoft.EntityFrameworkCore.Cosmos.Query.Internal.CosmosProjectionBindingExpressionVisitor.VisitMemberAssignment(MemberAssignment memberAssignment)
   at Microsoft.EntityFrameworkCore.Cosmos.Query.Internal.CosmosProjectionBindingExpressionVisitor.VisitMemberInit(MemberInitExpression memberInitExpression)
   at System.Linq.Expressions.MemberInitExpression.Accept(ExpressionVisitor visitor)
   at Microsoft.EntityFrameworkCore.Cosmos.Query.Internal.CosmosProjectionBindingExpressionVisitor.Visit(Expression expression)
   at Microsoft.EntityFrameworkCore.Cosmos.Query.Internal.CosmosProjectionBindingExpressionVisitor.Translate(SelectExpression selectExpression, Expression expression)
   at Microsoft.EntityFrameworkCore.Cosmos.Query.Internal.CosmosQueryableMethodTranslatingExpressionVisitor.TranslateSelect(ShapedQueryExpression source, LambdaExpression selector)
   at Microsoft.EntityFrameworkCore.Query.QueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at Microsoft.EntityFrameworkCore.Query.QueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at Microsoft.EntityFrameworkCore.Query.QueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at Microsoft.EntityFrameworkCore.Query.QueryCompilationContext.CreateQueryExecutor[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Storage.Database.CompileQuery[TResult](Expression query, Boolean 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 System.Runtime.CompilerServices.ConfiguredCancelableAsyncEnumerable`1.GetAsyncEnumerator()
 at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ToListAsync[TSource](IQueryable`1 source, CancellationToken cancellationToken)
   at Author.Query.Persistence.CountryService.GetCountriesDataAsync(Int32 languageId) in /src/QueryStack/Author.Query.Persistence/CountryService.cs:line 243
  at Author.Query.Persistence.CountryService.GetCountriesAsync(Int32 dftLanguageId, Int32 localeLangId) in /src/QueryStack/Author.Query.Persistence/CountryService.cs:line 228
  at Author.Query.Persistence.CountryService.GetAllCountriesAsync(LanguageDTO language) in /src/QueryStack/Author.Query.Persistence/CountryService.cs:line 164
  at GraphQL.DataLoader.DataLoaderBase`1.DispatchAsync(CancellationToken cancellationToken)
   at Author.Query.New.API.GraphQL.Resolvers.CountriesResolver.<>c__DisplayClass5_1.<<Resolve>b__3>d.MoveNext() in /src/QueryStack/Author.Query.New.API/GraphQL/Resolvers/CountriesResolver.cs:line 40
--- End of stack trace from previous location where exception was thrown ---
   at GraphQL.Types.ResolveFieldContext`1.TryAsyncResolve[TResult](Func`2 resolve, Func`2 error)
   --- End of inner exception stack trace ---

Can anyone help me here by providing their guidance to fix this issue?

Answer 1

You have a couple of issues here that are quite easy to fix, break the query int two halves the first to query the database and return list of partially populated CountryDTOs the second iterate through the list populating the missing items:

private async Task<List<CountryDTO>> GetCountriesDataAsync(int languageId)
{
            int pageNo = 1, pageSize = 100;

            var results = _dbContext.Countries // <- do not use await on db context
                    .Where(cc => cc.IsPublished.Equals(true)
                      && cc.LanguageId.Equals(languageId))
                    .Select(co => new {
                        co.CountryId,
                        co.DisplayName,
                        co.PNGImageId,
                        co.SVGImageId
                    })
                     .Skip((pageNo - 1) * pageSize) // <- use page size no 100
                     .Take(pageSize)
                     .ToListAsync();

            var images = await _cacheService.GetAllAsync("imagesCacheKey");

            return Task.FromResult( results.Select(co => new CountryDTO
            {
                Uuid = co.CountryId,
                PNGImagePath = images.FirstOrDefault(im => im.ImageId.Equals(co.PNGImageId))?.FilePath, // <- could be null so use ?.FilePath
                SVGImagePath = images.FirstOrDefault(im => im.ImageId.Equals(co.SVGImageId))?.FilePath,
                DisplayName = co.DisplayName,
                DisplayNameShort = co.DisplayName,
                Name = Helper.ReplaceChars(co.DisplayName),
                Path = Helper.ReplaceChars(co.DisplayName),
                CompleteResponse = true
            }).ToList());

}

I have created an anonymous type to hold the return from the database as opposed to adding additional field to the DTO for image ids and the likes. if you need more from the database just add the fields to the anonymous type in the context select statement.