Sequence contains more than one element ошибка

I’m having some issues with grabbing a list of type «RhsTruck» through Linq and getting them to display.

RhsTruck just has properites Make, Model, Serial etc…
RhsCustomer has properties CustomerName, CustomerAddress, etc…

I keep getting the error «Sequence contains more than one element» (of type InvalidOperationException). Any ideas? Am I approaching this the wrong way?

public RhsCustomer GetCustomer(string customerNumber)
{
    using (RhsEbsDataContext context = new RhsEbsDataContext() )
    {
        RhsCustomer rc = (from x in context.custmasts
                          where x.kcustnum == customerNumber
                          select new RhsCustomer()
                        {
                            CustomerName = x.custname,
                            CustomerAddress = x.custadd + ", " + x.custcity
                            CustomerPhone = x.custphone,
                            CustomerFax = x.custfax
                        }).SingleOrDefault();
        return rc;
    }
}

public List<RhsTruck> GetEquipmentOwned(RhsCustomer cust)
{
    using (RhsEbsDataContext context = new RhsEbsDataContext())
    {
        var trucks = (from m in context.mkpops
                      join c in context.custmasts
                        on m.kcustnum equals c.kcustnum
                      where m.kcustnum == cust.CustomerNumber
                      select new RhsTruck
                    {
                        Make = m.kmfg,
                        Model = m.kmodel,
                        Serial = m.kserialnum,
                        EquipID = m.kserialno1,
                        IsRental = false
                    }).ToList();
        return trucks;
    }
}

protected void Page_Load(object sender, EventArgs e)
{
    string testCustNum = Page.Request.QueryString["custnum"].ToString();
    
    RhsCustomerRepository rcrep = new RhsCustomerRepository();
    RhsCustomer rc = rcrep.GetCustomer(testCustNum);
    List<RhsTruck> trucks = rcrep.GetEquipmentOwned(rc);
    
    // I want to display the List into a Gridview w/auto-generated columns
    GridViewTrucks.DataSource = trucks;
    GridViewTrucks.DataBind();   
}

Источник

In this guide, we will explore the ‘Sequence Contains More Than One Matching Element’ error and how to resolve it. This error typically occurs when using LINQ (Language Integrated Query) in C#. We will delve into the root cause of this error, provide step-by-step solutions, and share expert tips to prevent it from reoccurring. We will also address frequently asked questions about this error.

Table of Contents

  • Understanding the Error
  • Step-by-Step Solution
  • Expert Tips to Prevent the Error
  • FAQs
  • Related Links

Understanding the Error

The ‘Sequence Contains More Than One Matching Element’ error occurs when using the SingleOrDefault or FirstOfDefault LINQ methods. These methods expect the input sequence to have only one matching element. If there are multiple matching elements in the sequence, an InvalidOperationException is thrown with the error message, «Sequence contains more than one matching element.»

Here’s an example of code that could cause this error:

List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 2 };
int result = numbers.SingleOrDefault(x => x == 2); // Error: Sequence contains more than one matching element.

In this example, the SingleOrDefault method is used to find the number 2 in the list of integers. However, there are two occurrences of the number 2 in the list, causing the error.

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Step-by-Step Solution

To resolve the ‘Sequence Contains More Than One Matching Element’ error, follow these steps:

Identify the cause of the error in your code.

Locate the SingleOrDefault or FirstOrDefault method call that is causing the error.

Replace the SingleOrDefault or FirstOrDefault method with an appropriate method, depending on your requirements.

If you want to retrieve all matching elements, use the Where method. This returns an IEnumerable of all matching elements.

List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 2 };
IEnumerable<int> results = numbers.Where(x => x == 2); // No error

If you want to retrieve the first matching element and don’t care about duplicates, use the First or FirstOrDefault method.

List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 2 };
int result = numbers.FirstOrDefault(x => x == 2); // No error: result = 2

Test your code to ensure the error is resolved.

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Expert Tips to Prevent the Error

Always use the SingleOrDefault and FirstOrDefault methods when you’re sure there will be only one matching element in the input sequence. If not, consider using the Where, First, or FirstOrDefault methods, as appropriate.

Add validation checks to ensure there are no duplicate elements in your input sequence if you need to use the SingleOrDefault or FirstOrDefault methods.

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FAQs

What is LINQ in C#?

LINQ (Language Integrated Query) is a feature introduced in C# 3.0 that allows developers to query data using a consistent syntax, regardless of the data source. LINQ can be used with collections, XML documents, databases, and other data sources. Learn more about LINQ here.

What is the difference between SingleOrDefault and FirstOrDefault?

SingleOrDefault and FirstOrDefault are LINQ methods in C#. While both methods return a single element from a sequence, they behave differently when the sequence contains more than one matching element. SingleOrDefault throws an error if there are multiple matching elements, while FirstOrDefault returns the first matching element without throwing an error.

What is the difference between First and FirstOrDefault?

Both First and FirstOrDefault are LINQ methods that return the first matching element from a sequence. The difference is in how they handle cases when no matching elements are found. First throws an InvalidOperationException if no matching elements are found, while FirstOrDefault returns the default value for the type (e.g., null for reference types or 0 for numeric types).

When should I use the Where method?

Use the Where method when you want to retrieve all matching elements from a sequence. The Where method returns an IEnumerable containing all the matching elements.

How do I handle an InvalidOperationException in C#?

To handle an InvalidOperationException, you can use a try-catch block to catch the exception and take appropriate action, such as displaying an error message or logging the exception.

try
{
    // Code that may throw InvalidOperationException
}
catch (InvalidOperationException ex)
{
    // Handle the exception
}

Back to top ↑

  • Microsoft Docs: LINQ in C#
  • Microsoft Docs: SingleOrDefault Method
  • Microsoft Docs: FirstOrDefault Method
  • Microsoft Docs: Where Method

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Источник

The query compiler throws an exception.

System.InvalidOperationException: Sequence contains more than one element
   at System.Linq.Enumerable.SingleOrDefault[TSource](IEnumerable`1 source)
   at Microsoft.EntityFrameworkCore.Query.RelationalQueryModelVisitor.BindMemberOrMethod[TResult](Func`4 memberBinder, IQuerySource querySource, IProperty property, Boolean bindSubQueries)
   at Microsoft.EntityFrameworkCore.Query.RelationalQueryModelVisitor.<>c__DisplayClass105_0`1.<BindMemberExpression>b__0(IProperty property, IQuerySource qs)
   at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.<>c__DisplayClass91_0`1.<BindMemberExpression>b__0(IReadOnlyList`1 ps, IQuerySource qs)
   at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.BindPropertyExpressionCore[TResult](Expression propertyExpression, IQuerySource querySource, Func`3 propertyBinder)
   at Microsoft.EntityFrameworkCore.Query.RelationalQueryModelVisitor.BindMemberExpression[TResult](MemberExpression memberExpression, Func`4 memberBinder, Boolean bindSubQueries)
   at Microsoft.EntityFrameworkCore.Query.ExpressionVisitors.RelationalEntityQueryableExpressionVisitor.VisitMember(MemberExpression node)
   at System.Linq.Expressions.MemberExpression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.ReplaceClauseReferences(Expression expression, IQuerySource querySource, Boolean inProjection)
   at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.VisitSelectClause(SelectClause selectClause, QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Query.RelationalQueryModelVisitor.VisitSelectClause(SelectClause selectClause, QueryModel queryModel)
   at Remotion.Linq.QueryModelVisitorBase.VisitQueryModel(QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.VisitQueryModel(QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Query.RelationalQueryModelVisitor.VisitQueryModel(QueryModel queryModel)
   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, IDiagnosticsLogger`1 logger, Type contextType)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass13_0`1.<Execute>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 Remotion.Linq.QueryableBase`1.GetEnumerator()
   at System.Collections.Generic.LargeArrayBuilder`1.AddRange(IEnumerable`1 items)
   at System.Collections.Generic.EnumerableHelpers.ToArray[T](IEnumerable`1 source)
   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at Test.Program.Main() in C:UsersUserDocumentsVisual Studio 2017ProjectsTestTestProgram.cs:line 34

Steps to reproduce

using Microsoft.Data.Sqlite;
using Microsoft.EntityFrameworkCore;
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;

namespace Test
{
    class Program
    {
        static void Main()
        {
            var connection = new SqliteConnection("Data Source=:memory:");
            connection.Open();

            var options = new DbContextOptionsBuilder<TestContext>()
                .UseSqlite(connection)
                .Options;

            using (var dbContext = new TestContext(options))
            {
                dbContext.Database.EnsureCreated();
            }

            using (var dbContext = new TestContext(options))
            {
                var query = dbContext.Outers
                    .OrderBy(o => Guid.NewGuid())
                    .SelectMany(o => o.Inners)
                    .Distinct()
                    .Select(i => i.Name);

                var result = query
                    .ToArray();
            }
        }
    }

    internal class TestContext : DbContext
    {
        public TestContext(DbContextOptions options)
            : base(options)
        {
        }

        public DbSet<Outer> Outers { get; set; }

        public DbSet<Inner> Inners { get; set; }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Outer>()
                .HasMany(a => a.Inners)
                .WithOne(t => t.Outer)
                .HasForeignKey(t => t.OuterId);
        }
    }

    internal class Outer
    {
        [Key]
        public int OuterId { get; set; }

        [Required]
        public string Name { get; set; }

        public List<Inner> Inners { get; set; }
    }

    internal class Inner
    {
        [Key]
        public int InnerId { get; set; }

        public int? OuterId { get; set; }
        public Outer Outer { get; set; }

        [Required]
        public string Name { get; set; }
    }
}

Test Solution: Test.zip

Further technical details

EF Core version: 2.1.0-rc1-final
Database Provider: Microsoft.Data.Sqlite
Operating system: Windows 10
IDE: Visual Studio Community 2017 15.7.1

Источник
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Sequence contains more than one matching element — one-to-mant with composite key

  • Question

  • When you try to create a one-to-many relationship from the use a composite key, I get the error «the sequence contains more than one matching element»

                modelBuilder.Entity<PracticePilotScoringInfo>()
                            .HasKey(info => new { info.DriverName, info.Control, info.VehicleClass, info.ScoringInfoId });
                modelBuilder.Entity<PracticeScoringInfo>()
                    .HasKey(info => info.Id)
                    .HasMany(info => info.PracticePilotScoringInfos)
                    .WithRequired(info => info.ScoringInfo)
                    .HasForeignKey(info => new { info.DriverName, info.Control, info.VehicleClass, info.ScoringInfoId });
    public class PracticeScoringInfo : ScoringInfo
    {
        public int GrandPrixId { get; set; }
        public GrandPrix GrandPrix { get; set; }

        public virtual ICollection<PracticePilotScoringInfo> PracticePilotScoringInfos { get; set; }
    }


    public class PracticePilotScoringInfo : PilotScoringInfo
    {
        public string DriverName { get; set; }
        public ControlType Control { get; set; }
        public string VehicleClass { get; set; }
        public Guid ScoringInfoId { get; set; }
        public virtual PracticeScoringInfo ScoringInfo { get; set; }
    }

    System.InvalidOperationException: Sequence contains more than one matching element
       в System.Linq.Enumerable.SingleOrDefault[TSource](IEnumerable`1 source, Func`2 predicate)
       в System.Data.Entity.ModelConfiguration.Edm.EdmEntityTypeExtensions.GetNavigationProperty(EdmEntityType entityType, PropertyInfo propertyInfo)
       в System.Data.Entity.ModelConfiguration.Edm.EdmModelExtensions.<>c__DisplayClass17.<GetNavigationProperty>b__12(EdmEntityType e)
       в System.Linq.Enumerable.WhereSelectListIterator`2.MoveNext()
       в System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
       в System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
       в System.Data.Entity.ModelConfiguration.Edm.EdmModelExtensions.GetNavigationProperty(EdmModel model, PropertyInfo propertyInfo)
       в System.Data.Entity.ModelConfiguration.Configuration.Properties.Navigation.NavigationPropertyConfiguration.ConfigureInverse(EdmAssociationType associationType, EdmModel model)
       в System.Data.Entity.ModelConfiguration.Configuration.Properties.Navigation.NavigationPropertyConfiguration.Configure(EdmNavigationProperty navigationProperty, EdmModel model, EntityTypeConfiguration entityTypeConfiguration)
       в System.Data.Entity.ModelConfiguration.Configuration.Types.EntityTypeConfiguration.ConfigureAssociations(EdmEntityType entityType, EdmModel model)
       в System.Data.Entity.ModelConfiguration.Configuration.Types.EntityTypeConfiguration.Configure(EdmEntityType entityType, EdmModel model)
       в System.Data.Entity.ModelConfiguration.Configuration.ModelConfiguration.ConfigureEntities(EdmModel model)
       в System.Data.Entity.DbModelBuilder.Build(DbProviderManifest providerManifest, DbProviderInfo providerInfo)
       в System.Data.Entity.DbModelBuilder.Build(DbConnection providerConnection)
       в System.Data.Entity.Internal.LazyInternalContext.CreateModel(LazyInternalContext internalContext)
       в System.Data.Entity.Internal.RetryLazy`2.GetValue(TInput input)
       в System.Data.Entity.Internal.LazyInternalContext.InitializeContext()
       в System.Data.Entity.Internal.LazyInternalContext.get_CodeFirstModel()
       в System.Data.Entity.Infrastructure.EdmxWriter.WriteEdmx(DbContext context, XmlWriter writer)
       в System.Data.Entity.Migrations.Extensions.DbContextExtensions.<>c__DisplayClass1.<GetModel>b__0(XmlWriter w)
       в System.Data.Entity.Migrations.Extensions.DbContextExtensions.GetModel(Action`1 writeXml)
       в System.Data.Entity.Migrations.Extensions.DbContextExtensions.GetModel(DbContext context)
       в System.Data.Entity.Migrations.DbMigrator..ctor(DbMigrationsConfiguration configuration, DbContext usersContext)
       в System.Data.Entity.Migrations.DbMigrator..ctor(DbMigrationsConfiguration configuration)
       в System.Data.Entity.Migrations.Design.ToolingFacade.BaseRunner.GetMigrator()
       в System.Data.Entity.Migrations.Design.ToolingFacade.UpdateRunner.RunCore()
       в System.Data.Entity.Migrations.Design.ToolingFacade.BaseRunner.Run()
    Sequence contains more than one matching element

    Thanks, help me please!

    • Edited by

      Sunday, September 1, 2013 1:34 PM

Answers

  • <copied>

    Sequence contains more than one matching element

    <end>

    What the message is telling you is that you have a composite-key possibly that is being duplicated there is more than one element with the same data. What that is, you’re going to have to find out.

    The same kind of error is thrown when doing a Linq query using SingleOrDefault() based on query criteria and more than one object is returned. The SingleOrDefault() means only one element should be returned, and if there is more than one element that meets
    the criteria, then the same type of error is thrown as above, which is an example.

    It’s just something you should be considering.

    • Marked as answer by
      Roman J. Barulin
      Sunday, September 1, 2013 8:52 PM

  • Thanks for answers!

    Looks like I’m not identified in Fluent API mapping. declaration a below is working fine.

    modelBuilder.Entity<ScoringInfo>()
            .HasKey(info => info.Id);

        modelBuilder.Entity<PracticeScoringInfo>()
            .HasKey(info => info.Id);

        modelBuilder.Entity<PilotScoringInfo>()
                    .HasKey(info => new { info.DriverName, info.Control, info.VehicleClass, info.ScoringInfoId });

        modelBuilder.Entity<PracticePilotScoringInfo>()
            .HasKey(info => new { info.DriverName, info.Control, info.VehicleClass, info.ScoringInfoId });

    • Marked as answer by
      Roman J. Barulin
      Sunday, September 1, 2013 2:39 PM

Источник

See more:

Hi there i’m having a problem with this wondering if anyone can help the error says:

System.InvalidOperationException: Sequence contains more than one element
Error Happens here: string active = @group.First() == item ? «active» : string.Empty;

Here my code:

<ul id="myTab" class="nav nav-tabs">
    @{ var group = Model.GroupBy(g => g.ReviewID).ToList(); }
    @foreach (var item in group)                
    {
      string active = @group.First() == item ? "active" : string.Empty;

      <li class="@active"><a href="#@Model.Where(a => a.ReviewID ==      item.Key).Single().Review.PersonID" data-toggle="tab"></a></li>
     }
     <li class="form-group pull-right">
        <div class="col-md-offset-1 col-md-12">
     <input type="submit" value="Submit" class="btn btn-primary btn-default" name="Add" />
    </div>
  </li>
</ul>

And below is my action Result

public ActionResult Index()
        {
            DateTime dateToday = DateTime.Now;
            DateTime firstOfThisMonth = new DateTime(dateToday.Year, dateToday.Month, 1);

            string name = User.Identity.Name;
            string newName = GetUserName(name);

            var unansweredReviews = from ur in db.Reviews
                                    where ur.PersonID == newName
                                    where ur.Responses.Any(s => s.ScoreID == null)
                                    select ur;

            if(unansweredReviews.Any())
            {
                return View(unansweredReviews.SelectMany(u => u.Responses).ToList());
            }

            var reviewForCurrentMonth = from cm in db.Reviews
                            where cm.PersonID == newName
                            where cm.DateTimeReviewed != null && cm.DateTimeReviewed <= firstOfThisMonth
                            select cm;

            if(reviewForCurrentMonth.Any())
            {
                Response.Redirect("~/Home/Index");
            }
            else
            {
                var getQuestions = db.Questions.Select(q => q.QuestionID);
                var peersToReview = db.People.Where(p => p.PersonID == newName).Single().MemberGroups.SelectMany(rg => rg.Members).ToList();

                foreach (var peers in peersToReview)
                {
                    Review reviews = new Review();
                    reviews.PersonID = newName;
                    reviews.ReviewPersonID = peers.PersonID;
                    foreach (var id in getQuestions)
                    {
                        Response responses = new Response();
                        responses.Review = reviews;
                        responses.QuestionID = id;
                        db.Responses.Add(responses);
                    }
                    db.Reviews.Add(reviews);
                } 
                db.SaveChanges();
            }
            return View();
        }

Updated 11-Aug-14 21:13pm

Your error seems to be generated from the next line of code:
«Model.Where(a => a.ReviewID == item.Key).Single().Review.PersonID«, and especial from using of Single() over a list of results.

So you should check that code and if there are more then one result, you should replace Single() with First().

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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+1 (416) 849-8900

Источник

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