我从 升级了数据层类库项目。NETCore 2.2 到 .NETCore3.1 并将 Nuget 包(如 EntityFrameWork Core(从 2.2.0 升级到 EFCore 3.1.0。
然后，我在验证以下代码时出现如下所述的错误：
法典：
private async Task<List<CountryDTO>> GetCountriesDataAsync(int languageId)
{
int pageNo = 1, pageSize = 100;
var images = await _cacheService.GetAllAsync("imagesCacheKey");
return await _dbContext.Countries
.Where(cc => cc.IsPublished.Equals(true)
&& cc.LanguageId.Equals(languageId))
.Select(co => new CountryDTO
{ Uuid = co.CountryId,
PNGImagePath = images.FirstOrDefault(im => im.ImageId.Equals(co.PNGImageId))
.FilePath,
SVGImagePath = images.FirstOrDefault(im => im.ImageId.Equals(co.SVGImageId))
.FilePath,
DisplayName = co.DisplayName,
DisplayNameShort = co.DisplayName,
Name = Helper.ReplaceChars(co.DisplayName),
Path = Helper.ReplaceChars(co.DisplayName),
CompleteResponse = true})
.Skip((pageNo - 1) * 100)
.Take(pageSize)
.ToListAsync();
}
错误：
When called from 'VisitLambda', rewriting a node of type 'System.Linq.Expressions.ParameterExpression' must return a non-null value of the same type. Alternatively, override 'VisitLambda' and change it to not visit children of this type.
---> System.InvalidOperationException: When called from 'VisitLambda', rewriting a node of type 'System.Linq.Expressions.ParameterExpression' must return a non-null value of the same type. Alternatively, override 'VisitLambda' and change it to not visit children of this type.
at System.Linq.Expressions.ExpressionVisitor.VisitAndConvert[T](T node, String callerName)
at System.Dynamic.Utils.ExpressionVisitorUtils.VisitParameters(ExpressionVisitor visitor, IParameterProvider nodes, String callerName)
at System.Linq.Expressions.ExpressionVisitor.VisitLambda[T](Expression`1 node)
at Microsoft.EntityFrameworkCore.Cosmos.Query.Internal.CosmosProjectionBindingExpressionVisitor.Visit(Expression expression)
at System.Dynamic.Utils.ExpressionVisitorUtils.VisitArguments(ExpressionVisitor visitor, IArgumentProvider nodes)
at System.Linq.Expressions.ExpressionVisitor.VisitMethodCall(MethodCallExpression node)
at Microsoft.EntityFrameworkCore.Cosmos.Query.Internal.CosmosProjectionBindingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
at Microsoft.EntityFrameworkCore.Cosmos.Query.Internal.CosmosProjectionBindingExpressionVisitor.Visit(Expression expression)
at Microsoft.EntityFrameworkCore.Cosmos.Query.Internal.CosmosProjectionBindingExpressionVisitor.VisitMember(MemberExpression memberExpression)
at Microsoft.EntityFrameworkCore.Cosmos.Query.Internal.CosmosProjectionBindingExpressionVisitor.Visit(Expression expression)
at Microsoft.EntityFrameworkCore.Cosmos.Query.Internal.CosmosProjectionBindingExpressionVisitor.VisitMemberAssignment(MemberAssignment memberAssignment)
at Microsoft.EntityFrameworkCore.Cosmos.Query.Internal.CosmosProjectionBindingExpressionVisitor.VisitMemberInit(MemberInitExpression memberInitExpression)
at System.Linq.Expressions.MemberInitExpression.Accept(ExpressionVisitor visitor)
at Microsoft.EntityFrameworkCore.Cosmos.Query.Internal.CosmosProjectionBindingExpressionVisitor.Visit(Expression expression)
at Microsoft.EntityFrameworkCore.Cosmos.Query.Internal.CosmosProjectionBindingExpressionVisitor.Translate(SelectExpression selectExpression, Expression expression)
at Microsoft.EntityFrameworkCore.Cosmos.Query.Internal.CosmosQueryableMethodTranslatingExpressionVisitor.TranslateSelect(ShapedQueryExpression source, LambdaExpression selector)
at Microsoft.EntityFrameworkCore.Query.QueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
at Microsoft.EntityFrameworkCore.Query.QueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
at Microsoft.EntityFrameworkCore.Query.QueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
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.Query.Internal.EntityQueryable`1.GetAsyncEnumerator(CancellationToken cancellationToken)
at System.Runtime.CompilerServices.ConfiguredCancelableAsyncEnumerable`1.GetAsyncEnumerator()
at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ToListAsync[TSource](IQueryable`1 source, CancellationToken cancellationToken)
at Author.Query.Persistence.CountryService.GetCountriesDataAsync(Int32 languageId) in /src/QueryStack/Author.Query.Persistence/CountryService.cs:line 243
at Author.Query.Persistence.CountryService.GetCountriesAsync(Int32 dftLanguageId, Int32 localeLangId) in /src/QueryStack/Author.Query.Persistence/CountryService.cs:line 228
at Author.Query.Persistence.CountryService.GetAllCountriesAsync(LanguageDTO language) in /src/QueryStack/Author.Query.Persistence/CountryService.cs:line 164
at GraphQL.DataLoader.DataLoaderBase`1.DispatchAsync(CancellationToken cancellationToken)
at Author.Query.New.API.GraphQL.Resolvers.CountriesResolver.<>c__DisplayClass5_1.<<Resolve>b__3>d.MoveNext() in /src/QueryStack/Author.Query.New.API/GraphQL/Resolvers/CountriesResolver.cs:line 40
--- End of stack trace from previous location where exception was thrown ---
at GraphQL.Types.ResolveFieldContext`1.TryAsyncResolve[TResult](Func`2 resolve, Func`2 error)
--- End of inner exception stack trace ---
任何人都可以在这里通过提供解决此问题的指导来帮助我吗？
您在这里有几个很容易解决的问题，将查询分成两半，第一部分查询数据库并返回部分填充的国家/地区 DTO 列表，第二个遍历填充缺失项目的列表：
private async Task<List<CountryDTO>> GetCountriesDataAsync(int languageId)
{
int pageNo = 1, pageSize = 100;
var results = _dbContext.Countries // <- do not use await on db context
.Where(cc => cc.IsPublished.Equals(true)
&& cc.LanguageId.Equals(languageId))
.Select(co => new {
co.CountryId,
co.DisplayName,
co.PNGImageId,
co.SVGImageId
})
.Skip((pageNo - 1) * pageSize) // <- use page size no 100
.Take(pageSize)
.ToListAsync();
var images = await _cacheService.GetAllAsync("imagesCacheKey");
return Task.FromResult( results.Select(co => new CountryDTO
{
Uuid = co.CountryId,
PNGImagePath = images.FirstOrDefault(im => im.ImageId.Equals(co.PNGImageId))?.FilePath, // <- could be null so use ?.FilePath
SVGImagePath = images.FirstOrDefault(im => im.ImageId.Equals(co.SVGImageId))?.FilePath,
DisplayName = co.DisplayName,
DisplayNameShort = co.DisplayName,
Name = Helper.ReplaceChars(co.DisplayName),
Path = Helper.ReplaceChars(co.DisplayName),
CompleteResponse = true
}).ToList());
}
我创建了一个匿名类型来保存来自数据库的返回，而不是向 DTO 添加图像 ID 等的附加字段。 如果您需要从数据库中获取更多信息，只需将字段添加到上下文选择语句中的匿名类型即可。
这个错误刚刚发生在我身上，对于未来的访问者来说，这是我做错的：
例如，我有两个模型：
public User
{
public int Id {get; set;}
public string Name {get; set;}
//just a silly method that does something
public string GetName()
{
return this.Name + "something"
}
}
public UserInfo
{
public int Id {get; set;}
// a bunch of other properties
}
在代码的某个地方，我使用自动映射器进行投影，例如
Mapper.ProjectTo<UserInfo>(Repository.Get().ByUserName(userId)).FirstOrDefault();
当我插入以某种方式破坏 projectTo 映射的GetName方法时，此错误When called from 'VisitLambda',...开始显示。
我的情况有点不同，但完全相同的错误：">当从'VisitLambda'调用时，重写类型为'System.Linq.Expressions.ParameterExpression'的节点必须返回相同类型的非空值">
但是，我的集合是分开的，我没有在同一数据库调用上运行投影。我检索了一个IQueryable<MyType>集合，然后检索了一个选择投影到我的视图模型。我也没有在我的投影中使用任何本地函数。
所以，发生的事情是我在同一投影中使用了两个不同的集合。我有一个IQueryable<DbSet<T>>集合，以及我从数据库中存储的某个DTO的不同列表。因此，它为"必须是相同类型的值"抛出异常是有道理的。
问题是使用另一个DTO列表：
collection.Select(s => new MyDataClass(s.Id, s.Name, otherDTOList.Find(...) ...
我的解决方案是在投影中使用外键引用，而不是尝试使用其他 DTO 列表，因为 FK 表数据是在连接中检索的：
collection.Select(s => new MyDataClass(s.Id, s.Name, s.MyFKClass.Find(...
奇怪的情况，如果有办法用两个集合做到这一点，请告诉我！