Update mongodb

Src/Asp.NetCore2/MongoDbTest/UnitTest/QueryLeftJoin2.cs

@@ -48,6 +48,10 @@ namespace MongoDbTest
                     cityName=city.Name
                 }).ToList();
             if (dt.First().schoolName != "清华大学" || dt.First().studentName != "张三" || dt.First().cityName != "北京") Cases.ThrowUnitError();
+
+           var dt2 = db.Queryable<Student>()
+            .LeftJoin<School>((s, sc) => s.SchoolId == sc.Id)
+            .Select((s, sc) => sc).ToList();
         }
         [SqlSugar.SugarTable("UnitStudentdu2s31")]
         public class Student : MongoDbBase

Src/Asp.NetCore2/SqlSugar.MongoDbCore/ExpToSql/ExpressionVisitor.cs

@@ -56,6 +56,8 @@ namespace SqlSugar.MongoDb
                     return new NewExpressionTractor(context, visitorContext).Extract(newNewExpression);
                 case ConditionalExpression conditionalExpression:
                     return new ConditionalExpressionTractor(context, visitorContext).Extract(conditionalExpression);
+                case ParameterExpression parameterExpression:
+                    return new ParameterExpressionTractor(context, visitorContext).Extract(parameterExpression);
                 default:
                     throw new NotSupportedException($"Unsupported expression: {expr.NodeType}");
             }

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

@@ -0,0 +1,55 @@
+using MongoDB.Bson;
+using System;
+using System.Collections.Generic;
+using System.Linq.Expressions;
+using System.Text;
+using System.Linq;
+namespace SqlSugar.MongoDb
+{
+    public class ParameterExpressionTractor
+    {
+        private MongoNestedTranslatorContext context;
+        private ExpressionVisitorContext visitorContext;
+
+        public ParameterExpressionTractor(MongoNestedTranslatorContext context, ExpressionVisitorContext visitorContext)
+        {
+            this.context = context;
+            this.visitorContext = visitorContext;
+        }
+
+        internal BsonValue Extract(ParameterExpression parameterExpression)
+        {
+            BsonValue bson = new BsonDocument();
+            if (IsSelect())
+            {
+                var isJoinTable = this.context?.queryBuilder?.JoinQueryInfos?.Any(s => s.ShortName.EqualCase(parameterExpression.Name)) == true;
+                foreach (var item in this.context.context.EntityMaintenance.GetEntityInfo(parameterExpression.Type).Columns)
+                {
+                    // 跳过忽略的列
+                    if (item.IsIgnore) continue;
+
+                    if (isJoinTable)
+                    {
+                        // 构建 "$x.y"
+                        string mongoFieldPath = "$" + parameterExpression.Name + "." + item.DbColumnName;
+
+                        // 设置别名
+                        string alias = item.DbColumnName; // 或者你自己定义别名逻辑
+
+                        ((BsonDocument)bson).Add(alias, mongoFieldPath);
+                    }
+                    else
+                    {
+                        ((BsonDocument)bson).Add(item.DbColumnName, 1);
+                    }
+                }
+            }
+            return bson;
+        }
+
+        private bool IsSelect()
+        {
+            return this.context.resolveType.IsIn(ResolveExpressType.SelectSingle, ResolveExpressType.SelectMultiple);
+        }
+    }
+}