LINQ to SQL query by string parameters

Question

Given: EF Core 1.0.1 and the following classes:

public class User { public int UserId {get;set;} public string Login {get;set;} public string Password {get;set;} } public class DataContext:DbContext { public DbSet<User> Users { get; set; } }

in the following code

 Datacontext dbcon = new DataContext(); var users = from p in dbcon.Users where p.Login=="login1" && p.Password=="pass1" select p; int number = users.Count();

an error occurs

InvalidOperationException: The "op_Equality" method.

why it happens? what should be done? complete exception description:

System.InvalidOperationException: "Op_Equality". at System.Linq.Expressions.Expression.GetMethodBasedBinaryOperator (ExpressionType binaryType, Expression left, Expression right, MethodInfo method, Boolean liftToNull) at System.Linq.Express_Enthal.Expression.Equal (Expression left, Expression right, Boolean liftToNull, method, Expression.Equal System.Linq.Expressions.Expression.MakeBinary (ExpressionType binaryType, Expression left, Expression of the right, Boolean liftToNull, MethodInfo method, LambdaExpression conversion) at Microsoft.EntityFrameworkCore.Query.ExpressionVisitors.Internal.NavigationRewritExEx of ours, 5888, 58, 17, 58, 58. Graphics.Query.ExpressionVisitors. .Expressions.BinaryExpression.Accept (ExpressionVisitor visitor) at System.Linq.Expressions.ExpressionVisitor.Visit (Expression node) at Microsoft.EntityFrameworkCore.Query.ExpressionVisitors.Internal.NavigationRewritingExpressionVisitor.VisitBinary (Insthedurant.Internal.NavigationRewritingExpressionVisitor.VisitBinary (Inventory.Internal.NavigationRewritingExpressionVisitor.VisitBinary (Supplicat.Internal.NavigationRewritingExpressionVisitor.VisitBinary (Incremental ReplicationVis.Internal.NavigationRewritingExpression node)) .Accept (ExpressionVisitor visitor) at System.Linq.Expressions.Expres sionVisitor.com (Expression) 2 transformation) at Microsoft.EntityFrameworkCore.Query.ExpressionVisitors.Internal.NavigationRewritingExpressionVisitor.NavigationRewritingQueryModelVisitor.VisitWhereClause(WhereClause whereClause, QueryModel queryModel, Int32 index) at Remotion.Linq.QueryModelVisitorBase.VisitBodyClauses(ObservableCollection 1 bodyClauses, queryModel queryModel) at Remotion.Linq.QueryModelVisitorBase.VisitQueryModel ( queryModel queryModel) at Microsoft.EntityFrameworkCore.Query.ExpressionVisitors.Internal.NavigationRewritingExpressionVisitor.Rewrite (queryModel queryModel, queryModel parentQueryModel) at Microsoft. Entity's a Expression query inodetyprovider 1.<CompileQuery>b__0() at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQueryCore[TFunc](Object cacheKey, Func 1 compiler) at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute [TResult] (Expression query) at System.Linq.Queryable.Count [TSource] (IQueryable`1 source) at SolidCRMCore.Startup . <> c. <b__2_0> d.MoveNext () in C: \ Users \ documents \ visual studio 2017 \ Projects \ SolidCRMCore \ SolidCRMCore \ Startup.cs: line 78 --- exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (Task task) at Microsoft.AspNetCore.Builder.Extensions.MapMiddelow.AnDebuggerNotification (Task task) at Microsoft.AspNetCore.Builder.Extensions.MapMddelow.AnDebuggerNotification (Task Task) - End of stack trace from previous loc ation where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (Task task) at Microsoft.AspNetCore.Diagn ..DeveloperExceptionPraframemad.Me.Mo.MoTe.MapToMeTeMeTeMeTeMeTeMeTeMeTeMeTeMeTeMeoMeToMetoramamak.

var users = db.Users.Where(x=>x.Login == "login1" && x.Password == "pass1").ToList();
IMHO, of course, but lambda syntax is easier to read in some cases
Error occurs when trying to check conditions on string fields
Yes, and attach to the question, please, the full text of the exception (along with the stack trace!) - without it, fortune telling on the coffee grounds turns out

user242389 user242389 one one · Answer 1 · 2017-03-30T11:33:51

like this:

  var users = con.Users.Where(p => p.Login.Equals(login)&&p.Password.Equals(password));

works, although the initial question, where to dig, remains open

Answer 2 · 2017-03-30T12:02:39

Apparently, this is an EF Core error at the query optimization stage. Try using a different version of the library.

If for some reason it is not possible to upgrade, use Workaround with a call to the Equals method:

 var users = from p in dbcon.Users where p.Login.Equals(login) && p.Password.Equals(password) select p;

PS if the error remains on the latest version of the library - the place on the githab is in its list of bugs

but dbcon.Users.Where (p => p.Login.Equals (login) && p.Password.Equals (password)) works;
@ user242389 No, from this side there can be no problem in principle.
The compiler generates exactly the same code for these two options.

Sv__t Sv__t 2.468 one eight 25 · Answer 3 · 2017-03-30T07:40:56

It may be worth doing this:

  DataContext dbcon = new DataContext(); // обрати внимание на эту строку, у тебя написано Datacontext вместо DataContext var users = from p in dbcon.Users where p.Login.Equals("login1") && p.Password.Equals("pass1") select p; int number = users.Count();

And, as I understand it, the DataContext class should look like this:

 public class DataContext: DbContext { public DbSet<Call> Calls { get; set; } public DbSet<User> Users { get; set; } }

The first line - made a mistake when retyping - is not the point;
I added the Users property - it is compiled with it, and in this example it works.

LINQ to SQL query by string parameters

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