ArgumentNull exception Entity Framework7

Question

Please I'm using this code to get entities from the sql server database

MyDbContext dbct = new MyDbContext (); IQueryable query = dbct.MyEntity;

But eache time I try to fetch my query I get those exceptions

System.ArgumentNullException: Value cannot be null. Parameter name: constructor at System.Linq.Expressions.Expression.New(ConstructorInfo constructor, IEnumerable1 arguments) at Microsoft.Data.Entity.Metadata.Internal.EntityMaterializerSource.CreateMaterializeExpression(IEntityType entityType, Expression valueBufferExpression, Int32[] indexMap) at Microsoft.Data.Entity.Query.ExpressionVisitors.Internal.MaterializerFactory.CreateMaterializer(IEntityType entityType, SelectExpression selectExpression, Func3 projectionAdder, IQuerySource querySource) at Microsoft.Data.Entity.Query.ExpressionVisitors.RelationalEntityQueryableExpressionVisitor.VisitEntityQueryable(Type elementType) at Microsoft.Data.Entity.Query.ExpressionVisitors.EntityQueryableExpressionVisitor.VisitConstant(ConstantExpression constantExpression) at System.Linq.Expressions.ConstantExpression.Accept(ExpressionVisitor visitor) at Microsoft.Data.Entity.Query.ExpressionVisitors.ExpressionVisitorBase.Visit(Expression expression) at Microsoft.Data.Entity.Query.EntityQueryModelVisitor.ReplaceClauseReferences(Expression expression, IQuerySource querySource, Boolean inProjection) at Microsoft.Data.Entity.Query.EntityQueryModelVisitor.CompileMainFromClauseExpression(MainFromClause mainFromClause, QueryModel queryModel) at Microsoft.Data.Entity.Query.RelationalQueryModelVisitor.CompileMainFromClauseExpression(MainFromClause mainFromClause, QueryModel queryModel) at Microsoft.Data.Entity.Query.EntityQueryModelVisitor.VisitMainFromClause(MainFromClause fromClause, QueryModel queryModel) at Remotion.Linq.Clauses.MainFromClause.Accept(IQueryModelVisitor visitor, QueryModel queryModel) at Remotion.Linq.QueryModelVisitorBase.VisitQueryModel(QueryModel queryModel) at Microsoft.Data.Entity.Query.EntityQueryModelVisitor.VisitQueryModel(QueryModel queryModel) at Microsoft.Data.Entity.Query.RelationalQueryModelVisitor.VisitQueryModel(QueryModel queryModel) at Microsoft.Data.Entity.Query.Internal.SqlServerQueryModelVisitor.VisitQueryModel(QueryModel queryModel) at Microsoft.Data.Entity.Query.EntityQueryModelVisitor.CreateQueryExecutor[TResult](QueryModel queryModel) at Microsoft.Data.Entity.Storage.Database.CompileQuery[TResult](QueryModel queryModel) --- End of stack trace from previous location where exception was thrown --- at Microsoft.Data.Entity.Query.Internal.QueryCompiler.<>c__DisplayClass18_01.<CompileQuery>b__0() at Microsoft.Data.Entity.Query.Internal.CompiledQueryCache.GetOrAddQuery[TResult](Object cacheKey, Func1 compiler) at Microsoft.Data.Entity.Query.Internal.QueryCompiler.CompileQuery[TResult](Expression query) at Microsoft.Data.Entity.Query.Internal.QueryCompiler.Execute[TResult](Expression query) at Microsoft.Data.Entity.Query.Internal.EntityQueryProvider.Execute[TResult](Expression expression) at Remotion.Linq.QueryableBase1.GetEnumerator() at Microsoft.Data.Entity.Internal.InternalDbSet1.System.Collections.Generic.IEnumerable.GetEnumerator() at System.Collections.Generic.List1..ctor(IEnumerable1 collection) at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)

There's really not much information in your question, but at a glance it looks like your entity type doesn't have a parameterless constructor. — CodeCaster
– CodeCaster, Commented Mar 21, 2016 at 11:46
thank you very much I forgot to add a parameterless constructor — anas M
– anas M, Commented Mar 21, 2016 at 11:51

CodeCaster · Accepted Answer · 2016-03-21 11:52:44Z

1

This really is an exception that Entity Framework should catch and wrap into a user-friendly exception, but what it's trying to tell you is this:

The entity type does not have a parameterless constructor defined.

Add it, and the exception will go away.

answered Mar 21, 2016 at 11:52

CodeCaster

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