使用谓词查询 EF

Question

我有以下（通用）存储库方法：

public async Task<TEntity> GetAsync(Expression<Func<TEntity, bool>> predicate, DateTime? asOf = null, IEnumerable<string> includeProperties = null,
                                    bool trackChanges = false)
{
    var query = Set.Include(includeProperties)
                   .AsOf(asOf);

    if (!trackChanges)
    {
        query = query.AsNoTracking();
    }

    return await query.SingleAsync(predicate);
}

执行此测试时，它工作正常

[Fact]
public static async Task GetStoffByStoffId_ReturnsEntity_OK_Test()
{
    // Arrange
    var dbContext = new SaiTestContext();
    IRepository<StoffEntity> repository = new Repository<StoffEntity>(dbContext);

    const string stoffId = "645106EF59801EE59EB22F1F93673380";

    // Act
    var entity = await repository.GetAsync(stoff => stoff.StoffId == stoffId);

    // Assert
    Assert.NotNull(entity);
}

当执行这个时

[Fact]
public static async Task GetStoffByStoffIdPredicate_ReturnsEntity_OK_Test()
{
    // Arrange
    var dbContext = new SaiTestContext();
    IRepository<StoffEntity> repository = new Repository<StoffEntity>(dbContext);

    var stoffUpdate = new StoffUpdateEntity
                      {
                          StoffId = "645106EF59801EE59EB22F1F93673380"
                      };

    Func<StoffEntity, StoffUpdateEntity, bool> stoffSeletor =
        (stoffEntity, updateEntity) => stoffEntity.StoffId == stoffUpdate.StoffId;

    // Act
    var entity = await repository.GetAsync(stoff => stoffSeletor(stoff, stoffUpdate));

    // Assert
    Assert.NotNull(entity);
}

这个异常被抛出

System.InvalidOperationException : The LINQ expression 'DbSet<StoffEntity>
    .Where(s => Invoke(__stoffSeletor_0, s[StoffEntity], __stoffUpdate_1)
    )' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to either AsEnumerable(), AsAsyncEnumerable(), ToList(), or ToListAsync(). See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.
   at Microsoft.EntityFrameworkCore.Query.QueryableMethodTranslatingExpressionVisitor.<VisitMethodCall>g__CheckTranslated|8_0(ShapedQueryExpression translated, <>c__DisplayClass8_0& )
   at Microsoft.EntityFrameworkCore.Query.QueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at Microsoft.EntityFrameworkCore.Query.RelationalQueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at EntityFrameworkCore.TemporalTables.Query.AsOfQueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at System.Linq.Expressions.MethodCallExpression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at Microsoft.EntityFrameworkCore.Query.QueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at Microsoft.EntityFrameworkCore.Query.RelationalQueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at EntityFrameworkCore.TemporalTables.Query.AsOfQueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at System.Linq.Expressions.MethodCallExpression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at Microsoft.EntityFrameworkCore.Query.QueryCompilationContext.CreateQueryExecutor[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Storage.Database.CompileQuery[TResult](Expression query, Boolean async)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.CompileQueryCore[TResult](IDatabase database, Expression query, IModel model, Boolean async)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass12_0`1.<ExecuteAsync>b__0()
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQueryCore[TFunc](Object cacheKey, Func`1 compiler)
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQuery[TResult](Object cacheKey, Func`1 compiler)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.ExecuteAsync[TResult](Expression query, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.ExecuteAsync[TResult](Expression expression, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ExecuteAsync[TSource,TResult](MethodInfo operatorMethodInfo, IQueryable`1 source, Expression expression, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ExecuteAsync[TSource,TResult](MethodInfo operatorMethodInfo, IQueryable`1 source, LambdaExpression expression, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.SingleAsync[TSource](IQueryable`1 source, Expression`1 predicate, CancellationToken cancellationToken)
   at Refdata.SAI.Data.Repositories.Repository`1.GetAsync(Expression`1 predicate, Nullable`1 asOf, IEnumerable`1 includeProperties, Boolean trackChanges) in C:\dev\Refdata.SAI\Source\Refdata.SAI.Data\Repositories\Repository.cs:line 75
   at Refdata.SAI.Data.Tests.Integration.RepositoryGetByPredicateTests.GetStoffByStoffIdPredicate_ReturnsEntity_OK_Test() in C:\dev\Refdata.SAI\Source\Refdata.SAI.Data.Tests.Integration\RepositoryGetByPredicateTests.cs:line 61
--- End of stack trace from previous location where exception was thrown ---

将函数作为参数传递时，是否可以修复第二个测试？

根本原因是我想从一个泛型类中使用这个函数，该函数是由protected abstract Func<TEntity, TUpdateEntity, bool> EntitySelector { get; } 在专用类中实现的。

Answer 1

表达式可以编译为函数，但任意函数不能转换回表达式。 stoffSelector 应该返回表达式，而不是函数：

Func<StoffUpdateEntity, Expression<Func<StoffEntity, bool>>> stoffSelector = 
    (stoffUpdate) => ((StoffEntity stoffEntity) => stoffEntity.StoffId == stoffUpdate.StoffId);

然后

// create predicate expression
var predicate = stoffSelector(stoffUpdate);

// use predicate
var entity = await repository.GetAsync(predicate);
    
    
    

或短版

var entity = await repository.GetAsync(stoffSelector(stoffUpdate));