如何使用功能“findone”在c＃中 [英] how to use function "findone" in c#

问题描述

我正在研究mongodb。

以下代码没问题。

I am studying mongodb.
the below code is ok.

using (var mongo = new Mongo(connectionstring))
            {
                mongo.Connect();
                var db = mongo.GetDatabase(dbName);
                var connection = db.GetCollection<Customer>();
                  
                Customer customer = connection.FindOne(x => x.CustomerID == "001");
                
                return customer;
            }

但是当使用Expression时，我无法得到结果。为什么？

But when using Expression,I can not get the result.Why?

using (var mongo = new Mongo(connectionstring))
            {
                mongo.Connect();
                var db = mongo.GetDatabase(dbName);
                var connection = db.GetCollection<Customer>();
                Func<Customer, bool> exp = x => x.CustomerID == "001";               
                Customer customer = connection.FindOne(exp);
                return customer;
            }

推荐答案

请参阅首先了解该怎么做

在MongoDatabase格式中您正在使用FindOne来自Mongo Collection的方法

NB

See First Know what to do
In MongoDatabase Format you are using FindOne method from a Mongo Collection
N.B.

connection.FindOne(IMongoQuery query);
It Means query usually a QueryDocument or constructed using the QueryBuilder
For this suggestion Use IMongoQuery

  IMongoQuery query = Query.EQ("CustomerID", "001");
  Customer customer = connection.FindOne(query);

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