Update mongoDb

Src/Asp.NetCore2/MongoDbTest/OrmTest/OrmTest.cs

@@ -97,6 +97,12 @@ namespace MongoDbTest
 
             var list9 = db.Queryable<OrderInfo>().OrderBy(it=>it.Name).OrderByDescending(it => it.Price).ToList();
 
+            var list10 = db.Queryable<OrderInfo>()
+                .Select(it=>new OrderInfo() { 
+                   Id=it.Id,
+                   Name=it.Name
+                }).ToDataTable();
+
             //测试生成SQL性能
             TestSqlBuilder(db);
         }

Src/Asp.NetCore2/SqlSugar.MongoDbCore/ExpToSql/VisitorItems/MemberInitExpressionTractor.cs

@@ -23,7 +23,33 @@ namespace SqlSugar.MongoDbCore
             {
                 return Update(expr);
             }
-            throw new Exception("");
+            else if(this._context.resolveType == ResolveExpressType.SelectSingle)
+            {
+                return Select(expr);
+            }
+            throw new NotSupportedException(this._context.resolveType+"");
+        }
+
+        private BsonValue Select(Expression expr)
+        {
+            var exp = expr as MemberInitExpression;
+            var projectionDocument = new BsonDocument();
+
+            // Iterate over the bindings in the MemberInitExpression
+            foreach (var binding in exp.Bindings)
+            {
+                if (binding is MemberAssignment assignment)
+                {
+                    var fieldName = assignment.Member.Name; // 原字段名
+
+                    // 将原字段名动态转换为 新字段名（例如：name -> name1）
+                    var newFieldName = fieldName ;
+
+                    // 将字段投影为 "新字段名" : "$原字段名"
+                    projectionDocument[newFieldName] = $"${fieldName}";
+                }
+            } 
+            return projectionDocument;
         }
 
         private  BsonValue Update(Expression expr)

Src/Asp.NetCore2/SqlSugar.MongoDbCore/MongoDb/SqlBuilder/MongoDbQueryBuilder.cs

@@ -1,7 +1,9 @@
 using MongoDB.Bson;
+using SqlSugar.MongoDbCore;
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Linq.Expressions;
 using System.Text;
 using System.Text.Json.Nodes;
 using System.Text.RegularExpressions;
@@ -113,6 +115,19 @@ namespace SqlSugar.MongoDb
                 }
             }
             #endregion
+
+            #region Select
+            if (this.SelectValue is Expression expression) 
+            {
+                var dos=MongoNestedTranslator.Translate(expression, new MongoNestedTranslatorContext() { 
+                    context = this.Context,
+                    resolveType=ResolveExpressType.SelectSingle
+                });
+                var json = dos.ToJson(UtilMethods.GetJsonWriterSettings());
+                operations.Add($"{{\"$project\": {json} }}"); 
+            }
+            #endregion
+
             sb.Append($"aggregate {this.GetTableNameString} ");
             sb.Append("[");
             sb.Append(string.Join(", ", operations));