C# 为包含嵌套实体的实体生成动态选择表达式
我有一个类,它的属性类型是另一个实体。如下所示:C# 为包含嵌套实体的实体生成动态选择表达式,c#,linq,linq-to-entities,entity-framework-6,expression-trees,C#,Linq,Linq To Entities,Entity Framework 6,Expression Trees,我有一个类,它的属性类型是另一个实体。如下所示: public class InspectionTopicDataAllViewModel { public Guid Id { get; set; } public Guid? UploadedFileId { get; set; } public int InspectionId { get; set; } public int InspectionTopicId { get; set; } publ
public class InspectionTopicDataAllViewModel
{
public Guid Id { get; set; }
public Guid? UploadedFileId { get; set; }
public int InspectionId { get; set; }
public int InspectionTopicId { get; set; }
public SparseDataViewModel SparseData { get; set; }
}
public class SparseDataViewModel : SparseData
{
}
我需要编写一个动态选择表达式,能够只选择我想要的列
我写这封信如下:
private static Func<InspectionTopicDataAll, InspectionTopicDataAllViewModel> GetSparseInitExpression(List<string> columns)
{
Expression<Func<InspectionTopicDataAll, InspectionTopicDataAllViewModel>> commonSelector =
x => new InspectionTopicDataAllViewModel()
{
Id = x.Id,
InspectionId = x.InspectionId,
InspectionTopicId = x.InspectionTopicId,
UploadedFileId = x.UploadedFileId,
};
// input parameter "x"
var xParameter = Expression.Parameter(typeof(InspectionTopicDataAll), "x");
var xNew = Expression.New(typeof(InspectionTopicDataAllViewModel));
var sNew = Expression.New(typeof(SparseDataViewModel));
var bindings = new List<MemberBinding>();
// create initializers
foreach (var column in columns)
{
Expression srcBody = xParameter;
foreach (var member in column.Split('.'))
{
srcBody = Expression.PropertyOrField(srcBody, member);
}
var destMember = srcBody as MemberExpression;
// property "Field1"
var propInfo = destMember?.Member as PropertyInfo;
if (propInfo != null)
{
bindings.Add(Expression.Bind(propInfo, srcBody));
}
}
var sInit = Expression.MemberInit(sNew, bindings);
var zeroth = ((MemberInitExpression)commonSelector.Body);
var param = commonSelector.Parameters[0];
List<MemberBinding> newBindings = new List<MemberBinding>(zeroth.Bindings.OfType<MemberAssignment>());
var spNestedType = typeof (InspectionTopicDataAllViewModel).GetProperty(nameof(SparseData));
newBindings.Add(Expression.Bind(spNestedType, sInit));
var newInit = Expression.MemberInit(xNew, newBindings);
var childSelector = Expression.Lambda<Func<InspectionTopicDataAll, InspectionTopicDataAllViewModel>>(newInit, xParameter);
return childSelector.Compile();
}
var model =
worksheetService.GetInspectionTopicData(inspectionTopicId, inspectionId, discrimintor, value)
.Select(GetCustomSelectExpression(columns));
使用此函数,我可以生成所需的表达式,如下所示:
x => new InspectionTopicDataAllViewModel()
{
Id = x.Id,
InspectionId = x.InspectionId,
InspectionTopicId = x.InspectionTopicId,
UploadedFileId = x.UploadedFileId,
SparseData = new SparseDataViewModel() {
MusteriNo = x.SparseData.MusteriNo,
MusteriAdi = x.SparseData.MusteriAdi,
CekNo = x.SparseData.CekNo,
Banka = x.SparseData.Banka,
CekTarihi = x.SparseData.CekTarihi,
Meblag = x.SparseData.Meblag,
PCN = x.SparseData.PCN,
Kesideci = x.SparseData.Kesideci}}}
但当我运行表达式时,会抛出以下错误:
类型的变量“x”
'InternalControl.Domain.Entities.InspectionTopicDataAll'
从作用域“”引用,但未定义它
我不知道如何修复此错误
更新:感谢@MBoros的帮助,以后可能需要这类代码,使用上述代码,即使代码可以工作,结果可以从数据库中检索,select语句也没有按预期工作,所有列都从数据库中获取,所以为了解决这个问题,我使用了下面的代码:希望能帮助其他尝试做这类事情的人
private static Expression<Func<InspectionTopicDataAll, InspectionTopicDataAllViewModel>> GetCustomSelectExpression(List<string> columns)
{
Expression<Func<InspectionTopicDataAll, InspectionTopicDataAllViewModel>> commonSelector =
x => new InspectionTopicDataAllViewModel()
{
Id = x.Id,
InspectionId = x.InspectionId,
InspectionTopicId = x.InspectionTopicId,
UploadedFileId = x.UploadedFileId,
};
// input parameter "x"
var xParameter = commonSelector.Parameters[0];
var xNew = Expression.New(typeof(InspectionTopicDataAllViewModel));
var sNew = Expression.New(typeof(SparseDataViewModel));
var bindings = new List<MemberBinding>();
// create initializers
foreach (var column in columns)
{
Expression srcBody = xParameter;
foreach (var member in column.Split('.'))
{
srcBody = Expression.PropertyOrField(srcBody, member);
}
var destColName = column.Substring(column.LastIndexOf('.')+1);
// property "Field1"
var propInfo = typeof(SparseDataViewModel).GetProperty(destColName);
if (propInfo != null)
{
bindings.Add(Expression.Bind(propInfo, srcBody));
}
}
var sInit = Expression.MemberInit(sNew, bindings);
var zeroth = ((MemberInitExpression)commonSelector.Body);
List<MemberBinding> newBindings = new List<MemberBinding>(zeroth.Bindings.OfType<MemberAssignment>());
var spNestedType = typeof (InspectionTopicDataAllViewModel).GetProperty(nameof(SparseData));
newBindings.Add(Expression.Bind(spNestedType, sInit));
var newInit = Expression.MemberInit(xNew, newBindings);
var childSelector = Expression.Lambda<Func<InspectionTopicDataAll, InspectionTopicDataAllViewModel>>(newInit, xParameter);
return childSelector;
}
您的
childSelector
不知道commonSelector
的x
参数。在表达式树中,参数是通过实例识别的,而不仅仅是通过名称识别的,因此这两个x
参数实际上是不同的(即使在调试视图中它们看起来相同)
最简单的解决办法可能是改变你的
// input parameter "x"
var xParameter = Expression.Parameter(typeof(InspectionTopicDataAll), "x");
到
这应该可以解决问题:)您的方法
工作表服务.GetInspectionTopicData
,这是Linq To Entities方法吗?还是Linq到对象?它返回IQueryable还是IEnumerable?它返回IQueryable
// input parameter "x"
var xParameter = Expression.Parameter(typeof(InspectionTopicDataAll), "x");
var xParameter = commonSelector.Parameters[0];