EF Core 2.1.2 and .net core 2.0 - Linq2Entities causes 'must be reducible node' error

asp.net-core-2.0 entity-framework entity-framework-core linq

Question

I investigated hours to find a solution or workaround for my problem. All I found is the error 'must be reducible node'is in combination with Linq Join or older EF versions. So I have to ask this question again.

Current Environment:

  • VS2017
  • .Net core 2.0 project
  • EntityFramework Core 2.1.2

My source code for this error is:

    // this query works...
var projectEfforts = from projectEntry in _context.ProjectTrackingEntry
                     where projectEntry.ProjectId == projectId
                     group projectEntry by new { projectEntry.Day.Year, projectEntry.Day.Month } into g
                     select new
                     {
                         PeDate = new DateTime(g.Key.Year, g.Key.Month, 1),
                         Month = g.Key,
                         MonthlyWorkingHours = g.Sum(x => x.WorkingHours)
                     };

// and here the query is executed with a valid result
string jsonprojectEfforts = Newtonsoft.Json.JsonConvert.SerializeObject(projectEfforts);

// following Linq will produce an error
var effHours = from projectEffort in projectEfforts
               where (projectEffort.PeDate < fromDate)
               select projectEffort.MonthlyWorkingHours;

// work with the result above will cause the 'must be reducible node' error
string jsoneffHours = Newtonsoft.Json.JsonConvert.SerializeObject(effHours);

For better understanding here is the result of the first Linq operation:

[{"PeDate":"2017-01-01T00:00:00","Month":{"Year":2017,"Month":1},"MonthlyWorkingHours":128.00} ,{"PeDate":"2018-01-01T00:00:00","Month":{"Year":2018,"Month":1},"MonthlyWorkingHours":40.00} ,{"PeDate":"2017-02-01T00:00:00","Month":{"Year":2017,"Month":2},"MonthlyWorkingHours":80.00} ,{"PeDate":"2017-03-01T00:00:00","Month":{"Year":2017,"Month":3},"MonthlyWorkingHours":88.00} ,{"PeDate":"2018-03-01T00:00:00","Month":{"Year":2018,"Month":3},"MonthlyWorkingHours":64.00} ,{"PeDate":"2017-04-01T00:00:00","Month":{"Year":2017,"Month":4},"MonthlyWorkingHours":104.00} ,{"PeDate":"2018-04-01T00:00:00","Month":{"Year":2018,"Month":4},"MonthlyWorkingHours":76.00} ,{"PeDate":"2017-05-01T00:00:00","Month":{"Year":2017,"Month":5},"MonthlyWorkingHours":16.00} ,{"PeDate":"2018-05-01T00:00:00","Month":{"Year":2018,"Month":5},"MonthlyWorkingHours":24.00} ,{"PeDate":"2017-06-01T00:00:00","Month":{"Year":2017,"Month":6},"MonthlyWorkingHours":60.00} ,{"PeDate":"2018-06-01T00:00:00","Month":{"Year":2018,"Month":6},"MonthlyWorkingHours":24.00} ,{"PeDate":"2017-07-01T00:00:00","Month":{"Year":2017,"Month":7},"MonthlyWorkingHours":48.00} ,{"PeDate":"2018-07-01T00:00:00","Month":{"Year":2018,"Month":7},"MonthlyWorkingHours":80.00} ,{"PeDate":"2017-08-01T00:00:00","Month":{"Year":2017,"Month":8},"MonthlyWorkingHours":104.00} ,{"PeDate":"2017-09-01T00:00:00","Month":{"Year":2017,"Month":9},"MonthlyWorkingHours":48.00} ,{"PeDate":"2017-10-01T00:00:00","Month":{"Year":2017,"Month":10},"MonthlyWorkingHours":72.00} ,{"PeDate":"2017-12-01T00:00:00","Month":{"Year":2017,"Month":12},"MonthlyWorkingHours":213.75}]

And the error for the second Linq operation (effHours) occurs with the try to serialize the result in JSON (last code line in above snippet):

at System.Linq.Expressions.Expression.ReduceAndCheck() at System.Linq.Expressions.Expression.ReduceExtensions() at System.Linq.Expressions.Compiler.StackSpiller.RewriteExtensionExpression(Expression expr, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.RewriteMemberExpression(Expression expr, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.RewriteMemberExpression(Expression expr, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.Add(Expression expression) at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.AddArguments(IArgumentProvider expressions) at System.Linq.Expressions.Compiler.StackSpiller.RewriteNewExpression(Expression expr, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.Add(Expression expression) at System.Linq.Expressions.Compiler.StackSpiller.RewriteBinaryExpression(Expression expr, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpressionFreeTemps(Expression expression, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.Rewrite[T](Expression1 lambda) at System.Linq.Expressions.Expression1.Accept(StackSpiller spiller) at System.Linq.Expressions.Compiler.StackSpiller.RewriteLambdaExpression(Expression expr) at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.Add(Expression expression) at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.AddArguments(IArgumentProvider expressions) at System.Linq.Expressions.Compiler.StackSpiller.RewriteMethodCallExpression(Expression expr, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.Add(Expression expression) at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.AddArguments(IArgumentProvider expressions) at System.Linq.Expressions.Compiler.StackSpiller.RewriteMethodCallExpression(Expression expr, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.Add(Expression expression) at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.AddArguments(IArgumentProvider expressions) at System.Linq.Expressions.Compiler.StackSpiller.RewriteMethodCallExpression(Expression expr, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpressionFreeTemps(Expression expression, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.Rewrite[T](Expression1 lambda) at System.Linq.Expressions.Expression1.Accept(StackSpiller spiller) at System.Linq.Expressions.Compiler.LambdaCompiler.Compile(LambdaExpression lambda) at System.Linq.Expressions.Expression1.Compile(Boolean preferInterpretation) at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.CreateExecutorLambda[TResults]() at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.CreateQueryExecutor[TResult](QueryModel queryModel) --- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.CompileQueryCore[TResult](Expression query, IQueryModelGenerator queryModelGenerator, IDatabase database, IDiagnosticsLogger1 logger, Type contextType) at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass13_01.<Execute>b__0() at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQueryCore[TFunc](Object cacheKey, Func1 compiler) at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query) at Remotion.Linq.QueryableBase`1.System.Collections.IEnumerable.GetEnumerator() at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IEnumerable values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty) at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value, Type objectType) at Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value, Type objectType) at Newtonsoft.Json.JsonConvert.SerializeObjectInternal(Object value, Type type, JsonSerializer jsonSerializer) at My.api.MyController.MyServiceMethod(Guid projectId, DateTime fromDate, DateTime toDate) in C:\Sources[...]MyController.cs:line 347


Because this is all under the hood, I don't know how to proceed with that problem. I am also satisfied with a workaround or some hints.

Can anybody help me?

1
2
7/17/2018 12:33:25 PM

Popular Answer

Your projectEfforts is not a collection. It's a query, and you are running it twice. The second time produces an error.

So your workaround is to run the query just once, and derive effHours from the results instead of making it a second query.

var projectEffortsQuery = from projectEntry in _context.ProjectTrackingEntry
                     where projectEntry.ProjectId == projectId
                     group projectEntry by new { projectEntry.Day.Year, projectEntry.Day.Month } into g
                     select new
                     {
                         PeDate = new DateTime(g.Key.Year, g.Key.Month, 1),
                         Month = g.Key,
                         MonthlyWorkingHours = g.Sum(x => x.WorkingHours)
                     };

var projectEfforts = projectEffortsQuery.ToList();
0
7/17/2018 12:32:38 PM


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