实现 query 模式

notes/helloshop/ordering-service-cqrs-query.md

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+# 实现 CQRS 中的 Query 模式
+
+在 CQRS 模式的全程是 Command Query Responsibility Segregation，即命令查询职责分离。在 CQRS 模式中，命令和查询是分开实现的，命令负责写操作，查询负责读操作，这样可以更好地实现单一职责原则，同时也可以更好地实现性能优化。
+
+https://learn.microsoft.com/zh-cn/azure/architecture/patterns/cqrs
+
+### 定义订单查询接口
+
+```csharp
+public interface IOrderQueries
+{
+    Task<OrderDetails> GetOrderAsync(int id);
+}
+```
+
+### 实现订单查询接口
+
+```csharp
+public class OrderQueries : IOrderQueries
+{
+    private readonly OrderingContext _context;
+
+    public OrderQueries(OrderingContext context)
+    {
+        _context = context;
+        dbContext.Database.SetConnectionString("db2_connection_string");
+    }
+
+    public async Task<OrderDetails> GetOrderAsync(int id)
+    {
+      // do something
+    }
+}
+```
+
+### 注册订单查询接口
+
+```csharp
+services.AddScoped<IOrderQueries, OrderQueries>();
+```
+
+### 使用订单查询接口
+
+```csharp
+public class OrderController : ControllerBase
+{
+    private readonly IOrderQueries _orderQueries;
+
+    public OrderController(IOrderQueries orderQueries)
+    {
+        _orderQueries = orderQueries;
+    }
+
+    [HttpGet("{id}")]
+    public async Task<IActionResult> GetOrderAsync(int id)
+    {
+        var order = await _orderQueries.GetOrderAsync(id);
+        return Ok(order);
+    }
+}
+```
+
+