MongoDB .Net驱动2.0拉(删除元素)

Question

你能用2.0驱动程序帮助我正确运行"拉(删除)".

我有一个这样的集合,我想删除第一个跟随者字段命名为fethiye的追随者.

{
  "_id": ObjectId("554e05dfc90d3d4dfcaa2aea"),
  "username": "bodrum",
  "followerList": [
    {
      "_id": ObjectId("554e0625a51586362c33c6df"),
      "follower": "fethiye",
      "avatar": "fethiye.png"
    },
    {
      "_id": ObjectId("554e0625a51586362c33c6df"),
      "follower": "izmir",
      "avatar": "izmir.png"
    }
  ]
} 

我该如何修复此查询？

var filter = new BsonDocument("username", "bodrum");
var update = Builders<Person>.Update.Pull("followerList:follower", "fethiye");
Person pr = collection.FindOneAndUpdateAsync(filter, update).Result;

谢谢.

Answer 1

使用过滤器删除数组元素时,需要使用PullFilter构建器而不是Pull(与整个元素匹配).

var collection = db.GetCollection<Person>("people");
var filter = new BsonDocument("username", "bodrum");
var update = Builders<Person>.Update.PullFilter("followerList",
    Builders<Follower>.Filter.Eq("follower", "fethiye"));
var result = collection.FindOneAndUpdateAsync(filter, update).Result;

或者更简洁一点,使用lambdas:

var update = Builders<Person>.Update.PullFilter(p => p.followerList,
                                                f => f.follower == "fethiye");
var result = collection
    .FindOneAndUpdateAsync(p => p.username == "bodrum", update).Result;

Answer 2

假设您有一个集合名称 Person，您可以使用 PullFilter 从数组中删除记录

var filterBuilder = Builders<Person>.Filter.Eq(person => person.username, "bodrum");

var updateBuilder = Builders<Person>.Update.PullFilter(p => p.followerList,
                       Builders<Person>.Filter.Eq(per => per.follower, "fethiye"));

var updateResult = collection.UpdateOne(filterBuilder, updateBuilder);

Console.WriteLine(
            $"MatchedCount: {updateResult.MatchedCount}, ModifiedCount: {updateResult.ModifiedCount}");

如果我们还需要删除过滤文档中的值数组，我们可以用这一行替换更新构建器

var updateBuilder = Builders<Person>.Update.PullFilter(p => p.followerList,
                   Builders<Person>.Filter.In(per => per.follower, new List<string> {"fethiye", "izmir"}));

也可以保存很多文档，updateOne 可以替换为 updateMany

var updateResult = collection.UpdateMany(filterBuilder, updateBuilder);