Question

我想在MongoDB中加入多个文档。我使用了以下代码，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();

Bellow是基础实体 我忘了添加基本实体模型

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

}

Bellow是错误消息

表达式'System.Collections.Generic.IEnumerable 1[Project.Communication.EntityModels.ProductWarehouseMap]' cannot be used for parameter of type 'System.Linq.IQueryable 1 [Project.Communication.EntityModels.ProductWarehouseMap]'方法'System.Linq.IQueryable 1[Project.Communication.EntityModels.ProductWarehouseMap] Where[ProductWarehouseMap](System.Linq.IQueryable 1 [Project.Communication.EntityModels .ProductWarehouseMap]，System.Linq.Expressions.Expression 1[System.Func 2 [Project.Communication.EntityModels.ProductWarehouseMap，System.Boolean]]）' 参数名称：arg0

Answer 1

您的错误消息使得它似乎使用了Where，但它不是（假设您显示的代码正是您尝试编译的代码）。不过，您可以尝试一些变体，例如

使用IEnumerable在内存中执行Select（）：

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：如果数据集很大，上述方法将花费很长时间并使用大量内存。

为了找到根本原因，您是否可以尝试此查询并让我知道它返回的内容：

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

如何加入多个文件？

1 个答案: