RavenDb是文档型数据库,但是我们常常也需要定义对象之间的关系,那RavenDb当中是如何处理的呢? RavenDb提供了优雅的解决方式,使用正确的话,可以减少数据开销以及网络拥堵 Denormalization 第一种就是反规范化,下面是一个订单的JSON格式 在Order这个订单当中我们把我们需要的客户信息(名字)也保存下来了,使用的时候,它直接就读出来了。 { // Order document with id: orders/1234 "Customer": { "Name": "Itamar", "Id": "customers/2345" }, Items: [ { "Product": { "Id": "products/1234", "Name": "Milk", "Cost": 2.3 }, } ] } 初始的类设计如下: public class Order { public string CustomerId { get; set; } public string[] SupplierIds { get; set; } public Referral Refferal { get; set; } public LineItem[] LineItems { get; set; } public double TotalPrice { get; set; } } public class Customer { public string Name { get; set; } public string Address { get; set; } public short Age { get; set; } public string HashedPassword { get; set; } } 在Order中持有下面这个反规范化的类,而不只是CustomerId public class DenormalizedCustomer { public int Id { get; set; } public string Name { get; set; } public string Address { get; set; } } Includes )RavenDb提供了这个Includes的功能去限制反规范化,上一种方式是直接保存了另外一个对象的一些属性,这种方式只是保存了一个引用,当根对象被加载的时候,和它关联的选项也会预加载。 我们可以这样做: var order = session.Include<Order>(x => x.CustomerId) .Load("orders/1234"); //这一句不会在服务端执行 var cust = session.Load<Customer>(order.CustomerId); )加载多个文档 同时加载"orders/1234", "orders/4321" var orders = session.Include<Order>(x => x.CustomerId) .Load("orders/1234", "orders/4321"); foreach (var order in orders) { // this will not require querying the server! var cust = session.Load<Customer>(order.CustomerId); } 另外一种用法: var orders = session.Query<Order>() .Customize(x => x.Include<Order>(o => o.CustomerId)) .Where(x => x.TotalPrice > ) .ToList(); foreach (var order in orders) { // this will not require querying the server! var cust = session.Load<Customer>(order.CustomerId); } 这里面有两个通道,当调用Load()方式时,调用了Results channel,第二个是 Includes channel,被包含的文档是通过它来返回的,并且保存在session cache当中。 )一对多Includes 一个订单,多个提供商 var order = session.Include<Order>(x => x.SupplierIds) .Load("orders/1234"); foreach (var supplierId in order.SupplierIds) { // this will not require querying the server! var supp = session.Load<Supplier>(supplierId); } )二级包含关系 二级包含关系是值,Order类的属性里面没有,是在Order类的属性Referral的属性当中有 public class Referral { public string CustomerId { get; set; } public double CommissionPercentage { get; set; } } var order = session.Include<Order>(x => x.Refferal.CustomerId) .Load("orders/1234"); // this will not require querying the server! var referrer = session.Load<Customer>(order.Refferal.CustomerId); 它也支持集合 var order = session.Include<Order>(x => x.Refferal.CustomerId) .Load("orders/1234"); // this will not require querying the server! var referrer = session.Load<Customer>(order.Refferal.CustomerId); )lucene query var orders = session.Advanced.LuceneQuery<Order2>() .Include(x => x.Customer2Id) .WhereGreaterThan(x => x.TotalPrice, ) .ToList(); foreach (var order in orders) { // this will not require querying the server! var cust2 = session.Load<Customer2>(order.Customer2Id); } var orders = session.Advanced.LuceneQuery<Order2>() .Include("CustomerId") .WhereGreaterThan(x => x.TotalPrice, ) .ToList(); foreach (var order in orders) { // this will not require querying the server! var cust2 = session.Load<Customer2>(order.Customer2Id); } Combining Approaches 这种是把前两种方式结合起来了 public class Order3 { public DenormalizedCustomer Customer { get; set; } public string[] SupplierIds { get; set; } public Referral Refferal { get; set; } public LineItem[] LineItems { get; set; } public double TotalPrice { get; set; } } var order = session.Include<Order3, Customer2>(x => x.Customer.Id) .Load("orders/1234"); // this will not require querying the server! var fullCustomer = session.Load<Customer2>(order.Customer.Id);