Question

这很好用：

return Members
          .FirstOrDefault(m => m.Agreement.Equals(agreement));

但如果找不到匹配项，则抛出异常：

 return Members
            .Include("Files")
            .FirstOrDefault(m => m.Agreement.Equals(agreement) &&
            !m.Files.Any(f => f.Status.Equals(12)));

那么当我使用Include时，如何获得first / default（可能为null）？

例外是：

意外的异常   System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.ConstantTranslator.TypedTranslate（ExpressionConverter   parent，ConstantExpression linq）at   System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator 1.Translate(ExpressionConverter parent, Expression linq) at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq) at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.EqualsTranslator.TypedTranslate(ExpressionConverter parent, BinaryExpression linq) at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator 1.Translate（ExpressionConverter   父母，表达linq）at   System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression（表达式   linq）at   System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateLambda（LambdaExpression   lambda，DbExpression输入）at   System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateLambda（LambdaExpression   lambda，DbExpression输入，DbExpressionBinding＆amp;绑定）   System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate（ExpressionConverter   parent，MethodCallExpression call，DbExpression＆amp;资源，   DbExpressionBinding＆安培; sourceBinding，DbExpression＆amp; lambda）   System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate（ExpressionConverter   parent，MethodCallExpression call）at   System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.SequenceMethodTranslator.Translate（ExpressionConverter   parent，MethodCallExpression call，SequenceMethod sequenceMethod）
  在   System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate（ExpressionConverter   parent，MethodCallExpression linq）at   System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator 1.Translate(ExpressionConverter parent, Expression linq) at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq) at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.NotTranslator.TypedTranslate(ExpressionConverter parent, UnaryExpression linq) at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator 1.Translate（ExpressionConverter   父母，表达linq）at   System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression（表达式   linq）at   System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.BinaryTranslator.TypedTranslate（ExpressionConverter   parent，BinaryExpression linq）at   System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator 1.Translate(ExpressionConverter parent, Expression linq) at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq) at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateLambda(LambdaExpression lambda, DbExpression input) at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateLambda(LambdaExpression lambda, DbExpression input, DbExpressionBinding& binding) at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, DbExpression& source, DbExpressionBinding& sourceBinding, DbExpression& lambda) at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate(ExpressionConverter parent, MethodCallExpression call) at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.SequenceMethodTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, SequenceMethod sequenceMethod) at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq) at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator 1.Translate（ExpressionConverter   父母，表达linq）at   System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression（表达式   linq）at   System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.AggregateTranslator.Translate（ExpressionConverter   parent，MethodCallExpression call）at   System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.SequenceMethodTranslator.Translate（ExpressionConverter   parent，MethodCallExpression call，SequenceMethod sequenceMethod）
  在   System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate（ExpressionConverter   parent，MethodCallExpression linq）at   System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator 1.Translate(ExpressionConverter parent, Expression linq) at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq) at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.Convert() at System.Data.Entity.Core.Objects.ELinq.ELinqQueryState.GetExecutionPlan(Nullable 1   forMergeOption）at   System.Data.Entity.Core.Objects.ObjectQuery 1.<>c__DisplayClass7.<GetResults>b__6() at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func 1   func，IDbExecutionStrategy executionStrategy，Boolean   startLocalTransaction，Boolean releaseConnectionOnSuccess）at   System.Data.Entity.Core.Objects.ObjectQuery 1.<>c__DisplayClass7.<GetResults>b__5() at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func 1   操作）   System.Data.Entity.Core.Objects.ObjectQuery 1.GetResults(Nullable 1   forMergeOption）at   System.Data.Entity.Core.Objects.ObjectQuery 1.<System.Collections.Generic.IEnumerable<T>.GetEnumerator>b__0() at System.Data.Entity.Internal.LazyEnumerator 1.MoveNext（）at   System.Linq.Enumerable.Single [TSource]（IEnumerable的1 source) at System.Data.Entity.Core.Objects.ELinq.ObjectQueryProvider.<GetElementFunction>b__3[TResult](IEnumerable 1   序列）   System.Data.Entity.Core.Objects.ELinq.ObjectQueryProvider.ExecuteSingle [TResult]（IEnumerable的1 query, Expression queryRoot) at System.Data.Entity.Core.Objects.ELinq.ObjectQueryProvider.System.Linq.IQueryProvider.Execute[TResult](Expression expression) at System.Data.Entity.Internal.Linq.DbQueryProvider.Execute[TResult](Expression expression) at System.Linq.Queryable.Count[TSource](IQueryable 1   源）

Answer 1

这个怎么样：

return Members
    .Include("Files")
    .Where(m => m.Agreement.Equals(agreement) &&
                m.Files != null &&
               !m.Files.Any(f => f.Status.Equals(12)))
    .FirstOrDefault();

Answer 2

尝试这种方式：

return Members.Include("Files")
                .FirstOrDefault(m => m.Agreement.Equals(agreement)
                 &&
                !m.Files.Any(f => f.Status==12));

我认为这会对你有帮助。

Answer 3

使用Microsoft.EntityFrameworkCore 3.1.7可以正常工作：

var myEntity = await dbContext.MyEntities.Include(x => x.MyOtherEntities).FirstOrDefaultAsync(x => x.Name == "Not existing name");

如何将FirstOrDefault与Include一起使用？

3 个答案: