MongoDB学习笔记~根据子集合里某个属性排序

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这个问题是这样的，有一个实体dog，里面有集合属性DogHistory，它里面有一些自己的属性，其中一个是SortNum，主要用来进行排序，而且这个排序可以影响主对象，即影响dog类，这个在mongodb里不容易实现，但也不是不能实现，我们需要分两步考虑这个问题，不过首先我们需要知道，mongodb里不支持子集合对象的子属性排序，但它支持子实体对象的子属性排序。

下面看一下数据结构

public class DogHistory
    {
        public bool IsHealth { get; set; }
        public Adderss Adderss { get; set; }
        public string HistoryName { get; set; }
        public string[] Foods { get; set; }
        public int SortNum { get; set; }
    }
    public class Dog : NoSqlEntity
    {
        public Des Des { get; set; }
        public string Title { get; set; }
        public string Type { get; set; }
        public string[] Foods { get; set; }
        public List<DogHistory> DogHistory { get; set; }
    }

其中Dog类子实体属性Des，它里面有属性sortNum，如果我们去排序，那是完全没有问题的，代码如下

           Console.WriteLine("--------------------子实体对象");
            var model3 = MongoDbClient.MongoManager<Dog>.Instance
              .Find(Builders<Dog>.Filter.Eq("DogHistory.HistoryName", "毛仔"))
              .SortBy(i => i.Des.SortNum).ToList();
            model3.ToList().ForEach(i =>
            {
                Console.WriteLine(i.Title + ":" + i.Title + ",sort:" + i.Des.SortNum);
            });

但如果希望根据DogHistory集合里的某个属性进行排序，那是不行的，虽然不行，但mongodb给出来了解决方案，对于集合类型可以通过索引下标的方式进行排序，这它是支持的。

下面代码展现了如何实现这种复杂的排序：

            var entityIndex = MongoDbClient.MongoManager<Dog>.Instance.Find(Builders<Dog>.Filter.Eq("DogHistory.HistoryName", "大毛")).FirstOrDefault();
            var index = entityIndex.DogHistory.FindIndex(i => i.HistoryName == "大毛");
            var model2 = MongoDbClient.MongoManager<Dog>.Instance
              .Find(Builders<Dog>.Filter.Eq("DogHistory.HistoryName", "大毛"))
              .SortBy(i => i.DogHistory[index].SortNum);
            model2.ToList().ForEach(i =>
            {
                Console.WriteLine(i.Title + ":" + i.DataStatus);
            });

结果与我们预期的一样，当然，如果是简单的字符数组类型，也是可以通过对数据下标元素排序的，呵呵。

测试结果：

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" 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