具有多个from子句的linq查询的方法语法

Question

I was trying to figure out how to replace the nested from clause to a method syntax. I was trying with .Select or .SelectMany, but I didn't manage to get the same result.

  var query = (from DirectToStoreStore s in dtsOrder.Stores
                        from DirectToStoreProduct p in s.Products
                        where p.DirectToStoreOrderLineID == directToOrderLineID
                        select p);

Answer 1

There's plenty of ways you could write it.

var query = dtsOrder.Stores.Cast<DirectToStoreStore>()
    .SelectMany(s => s.Products.Cast<DirectToStoreProduct>()
        .Where(p => p.DirectToStoreOrderLineID == directToOrderLineID)
    );

Though the casts may not be necessary, but they're only there since you explicitly declared them in your query. It'll probably be safe to remove them.