Update mongodb

Src/Asp.NetCore2/MongoDb.Ado.data/MongoDbCommand.cs

@@ -3,6 +3,7 @@ using System.Data.Common;
 using System.Data;
 using MongoDB.Bson;
 using MongoDB.Driver;
+using System.Linq;
 
 namespace MongoDb.Ado.data
 {
@@ -73,11 +74,24 @@ namespace MongoDb.Ado.data
             if (operation == "find")
             {
                 var filter = string.IsNullOrWhiteSpace(json) ? FilterDefinition<BsonDocument>.Empty : BsonDocument.Parse(json);
-                var document = collection.Find(filter).FirstOrDefault();
-                return document;
+
+                // 设置投影排除 "_id" 字段，确保返回的结果不包含 _id 字段
+                var projection = Builders<BsonDocument>.Projection.Exclude("_id");
+
+                // 执行查询并限制返回一条记录
+                var document = collection.Find(filter).Project(projection).FirstOrDefault();
+
+                // 如果查询到结果且文档非空，则获取第一个字段的值
+                if (document != null && document.Elements.Any())
+                {
+                    var firstElement = document.Elements.First();  // 获取第一个字段（列）
+                    return firstElement.Value;  // 返回该字段的值
                 }
 
-            throw new NotSupportedException("只支持 find 操作。");
+                return null; // 如果没有结果或没有字段，返回 null
+            }
+
+           return null;
         }
 
         protected override DbDataReader ExecuteDbDataReader(CommandBehavior behavior)

Src/Asp.NetCore2/MongoDbTest/AdoTest.cs

@@ -20,6 +20,8 @@ namespace MongoDbTest
         }
 
         private static void MongoDbCommandTest()
+        {
+            //ExecuteReader
             { 
                 var connection = new MongoDbConnection(DbHelper.SqlSugarConnectionString);
                 connection.Open();
@@ -34,6 +36,15 @@ namespace MongoDbTest
                 }
                 connection.Close();
             }
+            //ExecuteScalar
+            {
+                var connection = new MongoDbConnection(DbHelper.SqlSugarConnectionString);
+                connection.Open();
+                MongoDbCommand mongoDbCommand = new MongoDbCommand(" find b { age: { $gt: 31 } }", connection);
+                var value=mongoDbCommand.ExecuteScalar();
+                connection.Close();
+            }
+        }
 
         private static void MongoDbConnectionTest()
         {