在EFCore中使用DBContext查询时，什么会导致"Collection is read-only“异常？

Question

当我用我的DBContext执行一个基本的查询时，我得到了以下异常，并且我不能弄清楚它。它是一个控制台应用程序。

抛出的异常是：

        fail: Microsoft.EntityFrameworkCore.Query[10100]
          An exception occurred while iterating over the results of a query for context type 'JobAssist.Services.ArticleBankMgmt.Infrastructure.ArticleBankContext'.
          System.NotSupportedException: Collection is read-only.
             at System.Collections.ObjectModel.ReadOnlyCollection`1.System.Collections.Generic.ICollection<T>.Add(T value)
             at Microsoft.EntityFrameworkCore.Metadata.Internal.ClrICollectionAccessor`3.Add(Object entity, Object value, Boolean forMaterialization)
             at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.AddToCollection(INavigation navigation, InternalEntityEntry value, Boolean forMaterialization)
             at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalMixedEntityEntry.AddToCollection(INavigation navigation, InternalEntityEntry value, Boolean forMaterialization)
             at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.NavigationFixer.AddToCollection(InternalEntityEntry entry, INavigation navigation, InternalEntityEntry value, Boolean fromQuery)
             at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.NavigationFixer.SetReferenceOrAddToCollection(InternalEntityEntry entry, INavigation navigation, InternalEntityEntry value, Boolean fromQuery)
             at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.NavigationFixer.ToDependentFixup(InternalEntityEntry dependentEntry, InternalEntityEntry principalEntry, IForeignKey foreignKey, Boolean fromQuery)
             at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.NavigationFixer.InitialFixup(InternalEntityEntry entry, Boolean fromQuery)
             at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.NavigationFixer.TrackedFromQuery(InternalEntityEntry entry)
             at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntryNotifier.TrackedFromQuery(InternalEntityEntry entry)
             at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.MarkUnchangedFromQuery()
             at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.StartTrackingFromQuery(IEntityType baseEntityType, Object entity, ValueBuffer& valueBuffer)
             at Microsoft.EntityFrameworkCore.Query.QueryContext.StartTracking(IEntityType entityType, Object entity, ValueBuffer valueBuffer)
             at lambda_method(Closure , QueryContext , DbDataReader , ResultContext , ResultCoordinator )
             at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.CustomShaperCompilingExpressionVisitor.<PopulateIncludeCollection>g__ProcessCurrentElementRow|9_0[TIncludingEntity,TIncludedEntity](<>c__DisplayClass9_0`2& )
             at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.CustomShaperCompilingExpressionVisitor.PopulateIncludeCollection[TIncludingEntity,TIncludedEntity](Int32 collectionId, QueryContext queryContext, DbDataReader dbDataReader, ResultCoordinator resultCoordinator, Func`3 parentIdentifier, Func`3 outerIdentifier, Func`3 selfIdentifier, Func`5 innerShaper, INavigation inverseNavigation, Action`2 fixup, Boolean trackingQuery)
             at lambda_method(Closure , QueryContext , DbDataReader , ResultContext , Int32[] , ResultCoordinator )
             at Microsoft.EntityFrameworkCore.Query.Internal.QueryingEnumerable`1.Enumerator.MoveNext()
System.NotSupportedException: Collection is read-only.
   at System.Collections.ObjectModel.ReadOnlyCollection`1.System.Collections.Generic.ICollection<T>.Add(T value)
   at Microsoft.EntityFrameworkCore.Metadata.Internal.ClrICollectionAccessor`3.Add(Object entity, Object value, Boolean forMaterialization)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.AddToCollection(INavigation navigation, InternalEntityEntry value, Boolean forMaterialization)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalMixedEntityEntry.AddToCollection(INavigation navigation, InternalEntityEntry value, Boolean forMaterialization)
   at Microsoft.EntityFramew

代码是：

    var bank = articleBankContext.ArticleBanks.FirstOrDefault();
    Console.WriteLine(bank.Id);

在我的DBContext中，OnModelCreating代码是：

        protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        if (modelBuilder == null)
        {
            throw new ArgumentNullException(nameof(modelBuilder));
        }

        // Build the model
        modelBuilder.ApplyConfiguration(new ClientRequestEntityTypeConfiguration());

        modelBuilder.Entity<ArticleBank>(ab =>
        {
            ab.OwnsMany(ab => ab.ArticleTags, at =>
            {
                at.WithOwner();
                at.Property<DateTime>("CreatedDate");
                at.Property<DateTime>("UpdatedDate");
                at.ToTable("ArticleBankTags");
            });
        });

        modelBuilder.Entity<ArticleBank>(ab =>
        {
            ab.OwnsMany(ab => ab.Sources, s =>
            {
                s.WithOwner();
                s.Property<DateTime>("CreatedDate");
                s.Property<DateTime>("UpdatedDate");
                s.ToTable("ArticleBankSources");
            });
        });

        modelBuilder.Entity<Article>().OwnsOne(a => a.JSeeker).OwnsOne(a => a.Name);

        modelBuilder.Entity<Article>().OwnsMany(a => a.Ratings, ar => ar.ToTable("ArticleRatings").OwnsOne(ar => ar.JSeeker).OwnsOne(js => js.Name));
        modelBuilder.Entity<Article>().OwnsOne(a => a.Source).WithOwner();
        modelBuilder.Entity<Article>().OwnsMany(a => a.Tags).WithOwner();

        modelBuilder.Entity<ArticleBank>().HasMany(s => s.Articles);

        ////Create Shadow Properties
        modelBuilder.Entity<ArticleBank>().Property<DateTime>("CreatedDate");
        modelBuilder.Entity<ArticleBank>().Property<DateTime>("UpdatedDate");
        modelBuilder.Entity<Article>().Property<DateTime>("CreatedDate");
        modelBuilder.Entity<Article>().Property<DateTime>("UpdatedDate");
        modelBuilder.Entity<Article>().ToTable("ArticleBankArticles");
    }

我怎么知道他们说的是什么“只读集合”？在解决方案中的其他项目中，我没有遇到过类似的问题。我有一个"PrePopulateDB()“，它实际上使用相同的上下文并将适当的数据添加到数据库中。

以下是ArticleBanK中的声明：

我在构造函数中创建列表。

private readonly List<ArticleTag> _articleTags; 
public IEnumerable<ArticleTag> ArticleTags => _articleTags.AsReadOnly(); /
private readonly List<Article> _articles; 
public IEnumerable<Article> Articles => _articles.AsReadOnly();

此外，奇怪的是，在DBContext.Model.DebugView中没有Sources属性的字段：

  EntityType: ArticleBank
    Navigations:
      Articles (_articles, IEnumerable<Article>) Collection ToDependent Article
      ArticleTags (_articleTags, IEnumerable<ArticleTag>) Collection ToDependent ArticleBank.ArticleTags#ArticleTag
        Annotations:
          EagerLoaded: True
      Sources (no field, IEnumerable<ArticleSource>) Collection ToDependent ArticleBank.Sources#ArticleSource
        Annotations:
          EagerLoaded: True

Answer 1

我发现了问题所在。

我没有按惯例行事。我的导航字段(源)和(_articleSources)的属性不对齐。