在Entity Framework 2.0中使用Dynamic Linq Core创建包含列表的对象
我有以下两个类：
public Part {
public string PartNumber {get; set;}
public string Description {get; set;}
public List<Warehouse> Warehouses {get; set;}
}
public Warehouse {
public string PartNumber {get; set;}
public string WarehouseName {get; set;}
public int Quantity {get; set;}
public int ReorderPoint {get; set;}
}使用实体框架核心2.0，我使用一对多关系将它们关联起来。使用Dynamic Linq Core，我尝试创建一个查询，返回PartNumber、描述以及仓库列表中唯一属性为WarehouseName的特定部件的列表，理想情况下如下所示：
List<string> fields = new List<string> {"PartNumber", "Description", "Warehouses.WarehouseName"};
var _dataSet = dbContext.Parts.Include(x => x.Warehouses);
var data = _dataSet.Where("PartNumber = \"Part1234\"").Select("new (" + String.Join(",", fields) + ")").ToDynamicArray();但我收到这个错误：“类型‘List`1’中不存在属性或字段'Warehouse‘”。如果我这样做，它工作得很好：
var data = _dataSet.Where("PartNumber = \"Part1234\"").Select(x => new Part
{
PartNumber = x.PartNumber,
Description = x.Description,
Warehouses = x.Warehouses.Select(y => new Warehouse { Warehouse = y.Warehouse }).ToList()
}).Single();问题是我希望它是动态的，这样用户就可以从Part和Warehouse类传入他们想要获取的字段列表，而不必修改select来为那些特定的字段构建它。
Stack Overflow用户
发布于 2019-08-22 16:16:47
您需要支持Warehouses上的子查询。我将复制this answer中列出的相关步骤
- 在
ParseAggregateExpression ParseAggregate(Expression instance，Type elementType，string methodName，int Expression)中添加以下内容{ // Change starts var originalIt = it；var originalOuterIt = outerIt；// Change ends here outerIt = it；ParameterExpression innerIt = Expression.Parameter(elementType，elementType.Name)；it = innerIt；Expression[] args = ParseArgumentList()；// Change starts it =；=；//更改在此结束... } - 将
Select和ToList添加到IEnumerableSignatures中，并在ParseAggregate中分别添加条件：
接口IEnumerableSignatures { ...空选择(对象选择器)；空ToList()；... }表达式ParseAggregate(表达式实例，类型elementType，字符串methodName，整型errorPos) { ...如果(signature.Name == "Min“|| signature.Name == "Max”|| signature.Name == "Select") ... }
- Finally，您的查询将是：
static void Main() { //示例数据var Warehouse =新列表{新仓库{ WarehouseName = "NY1"，数量= 10 }，新仓库{ WarehouseName = "NY2"，数量= 100 } }；var parts =新列表{ PartNumber = "1"，Description = "Hammer"，Warehouse =Warehouse} }；//查询var结果=部件.Select(@“PartNumber (Warehouses.Select，Description，Warehouses.Select(WarehouseName).ToList() as WarehouseNames )")；}
https://stackoverflow.com/questions/49823411
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