如何加入多个文件？

Question

我想加入MongoDB中的多个文档。我使用了下面的代码，但它不起作用。我做错了吗？我添加了包含Id的基本实体模型。

var products = _productRepository.GetCollection(_dbContext); 
var prodWarhoseMapping = _productWarehouseMapRepository.GetCollection(_dbContext); 
var warhouses = _warehouseRepository.GetCollection(_dbContext); 

public class Product:BaseEntity 
{ 
    public string product_code { get; set; } 
    public decimal fat_tax { get; set; } 
} 

public class ProductWarehouseMap :BaseEntity 
{ 
    public ObjectId product_id { get; set; } 
    public ObjectId warehouse_id { get; set; } 
    public int qty { get; set; } 
    public decimal price { get; set; } 
} 
public class Warehouse :BaseEntity 
{ 
    public ObjectId supplier_id { get; set; } 
    public string warehouse_code { get; set; } 
    public string name { get; set; } 
    public string email { get; set; } 
    public string phone { get; set; } 
    public string street_address { get; set; } 
    public string city { get; set; } 
    public string postal_code { get; set; } 
    public string region { get; set; } 
    public string country { get; set; } 
    public string manager_name { get; set; } 
    public string fax { get; set; } 
} 

//works proper 
var query1 = (from p in products 
      join pm in prodWarhoseMapping on p._id equals pm.product_id 
         select new 
         { 
          Products = p, 
          ProductMapping = pm, 
         }).ToList(); 

//Getting error 
var query = (from p in products 
    join pm in prodWarhoseMapping on p._id equals pm.product_id 
    join wh in warhouses on pm.warehouse_id equals wh._id 
    select new 
    { 
     Products = p, 
     ProductMapping = pm, 
     Warehouse = wh 
    }).ToList(); 

娄是基本实体 我忘了添加碱实体模型

public class BaseEntity 
{ 
    [BsonIgnoreIfDefault] 
    public ObjectId _id { get; set; } 

} 

娄是错误消息

类型的“表达System.Collections.Generic.IEnumerable 1[Project.Communication.EntityModels.ProductWarehouseMap]' cannot be used for parameter of type 'System.Linq.IQueryable 1 [Project.Communication.EntityModels.ProductWarehouseMap]'of method'System.Linq.IQueryable 1[Project.Communication.EntityModels.ProductWarehouseMap] Where[ProductWarehouseMap](System.Linq.IQueryable 1 [Projec t.Communication.EntityModels.ProductWarehouseMap]，System.Linq.Expressions.Expression 1[System.Func 2 Project.Communication.EntityModels.ProductWarehouseMap，System.Boolean]）” 参数名：为arg0

Answer 1

你的错误消息，使得它看起来Where被使用，但它不是（假设你所展示的代码正是你试图编译的东西）。不过，你可以使用IEnumerable的尝试一些变化，例如

执行选择（）内存：

var query = (from p in products 
    join pm in prodWarhoseMapping on p._id equals pm.product_id 
    join wh in warhouses on pm.warehouse_id equals wh._id) 
    .AsEnumerable() 
    .Select(s => new 
    { 
     Products = p, 
     ProductMapping = pm, 
     Warehouse = wh 
    }).ToList(); 

或者使用AsQueryable()

var query = (from p in products.AsQueryable() 
    join pm in prodWarhoseMapping.AsQueryable() on p._id equals pm.product_id 
    join wh in warhouses.AsQueryable() on pm.warehouse_id equals wh._id 
    select new 
    { 
     Products = p, 
     ProductMapping = pm, 
     Warehouse = wh 
    }).ToList(); 

编辑：上述方法将需要很长时间和使用如果数据集很大，则会有很多内存。

为了找到根本原因，你可以试试这个查询，并让我知道它返回：

var query2 = (from pm in prodWarhoseMapping 
     join wh in warhouses on pm.warehouse_id equals wh._id 
        select new 
        { 
         ProductMapping = pm, 
         Warehouse = wh,        
        }).ToList();