c# - Linq、OData 和 WCF : “the method join is not supported”

Question

我正在尝试从多个表中恢复和显示数据。 o 我已经完成了这样的多重连接:

var prod = from product in context.PRODUCT
    join islocated in context.ISAUDITEDIN on product.PRODUCT_ID equals islocated.PRODUCT_ID
    join location in context.LOCATION on islocated.LOCATION_ID equals location.LOCATION_ID
    orderby location.LOCATION_ID
    group new
    {
       Location_ID = location.LOCATION_ID,
       Product_ID = product.PRODUCT_ID
    } by location.LOCATION_ID into locat
    select new {
       Location_ID = locat.Key,
       Product = locat
    };

其中 context 是导致 Web 服务调用的 OData。该链接有效:当我进行简单选择时，我能够恢复数据。然后，我想显示结果中的数据。所以我创建了一个字典:

Dictionary<string,List<ProductModel>> dict = new Dictionary<string,List<ProductModel>>();
foreach (var locat in prod) {
    List<ProdctModel> products = new List<ProductModel>();
    foreach (var p in locat.Product)
    {
        products.Add(new ProductModel(p.Location_ID, p.Product_ID));
    }
    dict.Add(locat.Location_ID.ToString(), products);
}

其中 ProductModel 是一个像这样的简单类:

public class ProdctModel
{
    public int locationID{get; set;}
    public int productID{get; set;}
    public ProdctModel(int location_ID, int product_ID)
    {
        this.locationID = location_ID;
        this.productID = product_ID;
    }
}

但是当我运行它时，我得到了以下信息:

“the method join is not supported”
Ligne 131 :            Dictionary<string,List<ProdctModel>> dict = new Dictionary<string,List<ProdctModel>>();
Ligne 132 :            foreach (var locat in prod) {

如何解决？我已经通过使用方法 .Expand() 而不是 join 看到了一些东西，但我不知道如何使用它:你能帮我吗？

谢谢!

Answer 1

我从未将 odata 与 linq 一起使用，但我假设您不能加入不同的远程资源。尝试先将对象获取到内存，然后再进行连接:

var products = context.PRODUCT.ToList();
var islocateds = context.ISAUDITEDIN.ToList();
var locations = context.LOCATION.ToList();


var prod = from product in products
                       join islocated in islocateds on product.PRODUCT_ID equals islocated.PRODUCT_ID
                       join location in locations on islocated.LOCATION_ID equals location.LOCATION_ID
                       orderby location.LOCATION_ID
                       group new
                       {
                           Location_ID = location.LOCATION_ID,
                           Product_ID = product.PRODUCT_ID
                       } by location.LOCATION_ID into locat
                       select new {
                           Location_ID = locat.Key,
                           Product = locat
                       };

请记住，这将下载所有 3 个表格。

编辑此外，您在创建字典时遇到异常的原因是“prod”变量是一个 IEnumerable - 它仅在您执行“foreach”或类似操作时执行请求。