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+# 分页排序和多条件查询
+
+## 分页参数
+
+请求应使用 GET 方法
+
+```shell
+http://localhost:8080/api/products?keyword=test&pagenumber=1&pagesize=5&orderby=id desc,price asc
+```
+
+响应返回如下
+
+```json
+{
+    "totalCount": 100,
+    "items": [
+        {
+            "id": 1,
+            "name": "test",
+            "price": 100
+        },
+        {
+            "id": 2,
+            "name": "test",
+            "price": 200
+        }
+    ]
+}
+```
+
+## 分页请求模型
+
+```csharp
+public class PagedAndSortedRequest : PagedRequest
+{
+    public string? OrderBy { get; init; }
+}
+```
+
+## 分页响应模型
+
+```csharp
+public class PagedResponse<T>(IReadOnlyList<T> items, int totalCount)
+{
+    public IReadOnlyList<T> Items { get; init; } = items;
+
+    public int TotalCount { get; init; } = totalCount;
+}
+```
+
+## 扩展 IQueryable 以便通过属性名称排序
+
+```shell
+QueryableOrderByExtensions.cs
+```
+
+将字符串条件转化为排序表达式
+
+```csharp
+IOrderedQueryable<TSource> OrderBy(IQueryable<TSource> source, string propertyName)
+```
+
+## 扩展 IQueryable 以便搜索和排序
+
+```shell
+QueryableExtensions.cs
+```
+
+扩展分页和排序方法
+
+```csharp
+IQueryable<TEntity> SortBy<TEntity>(this IQueryable<TEntity> query, string? orderBy = null);
+IQueryable<TEntity> PageBy<TEntity>(this IQueryable<TEntity> query, PagedRequest pagedRequest)
+IQueryable<TEntity> SortAndPageBy<TEntity>(this IQueryable<TEntity> query, PagedAndSortedRequest? pagedAndSortedRequest = null);
+```
+
+再扩展一个 WhereIf 条件查询
+
+```csharp
+IQueryable<TSource> WhereIf<TSource>(this IQueryable<TSource> source, bool condition, Expression<Func<TSource, bool>> predicate);
+```
+
+## 在 API 控制器中使用扩展方法
+
+```csharp
+[HttpGet]
+[Authorize(IdentityPermissions.Users.Default)]
+public async Task<ActionResult<PagedResponse<UserListItem>>> GetUsers([FromQuery] UserListRequest model)
+{
+    IQueryable<User> users = dbContext.Set<User>();
+
+    if (model.Keyword is not null)
+    {
+        users = users.Where(e => e.UserName != null && e.UserName.Contains(model.Keyword));
+    }
+
+    users = users.WhereIf(model.PhoneNumber is not null, e => e.PhoneNumber == model.PhoneNumber);
+
+    var pagedUsers = users.SortAndPageBy(model);
+
+    var list = new List<UserListItem>();
+
+    return new PagedResponse<UserListItem>(mapper.Map<List<UserListItem>>(await pagedUsers.ToListAsync()), await users.CountAsync());
+}
+```