Update mongodb

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

@@ -198,6 +198,13 @@ namespace MongoDbTest
 
             var list25 = db.Queryable<Student>().Where(it => it.Name == it.Name && it.Name=="a").ToList();
             if (list25.Count!=1||list25.First().Name != "a") Cases.ThrowUnitError();
+
+            var list26 = db.Queryable<Student>().Select(it => new  
+            {
+                Age1 =  it.Age > 0? it.Age: 1,
+                Age2 =SqlFunc.IIF( it.Age > 0 , it.Age ,1),
+            }).ToList();
+            if (list26.First().Age1 != list26.First().Age2) Cases.ThrowUnitError();
         }
         [SqlSugar.SugarTable("UnitStudent1231sds3z1")]
         public class Student : MongoDbBase

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

@@ -60,6 +60,10 @@ namespace SqlSugar.MongoDb
                 {
                     projectionDocument[fieldName] = json;
                 }
+                else if (memberAssignment.Expression is MethodCallExpression callExpression&&callExpression.Method.Name==nameof(SqlFunc.IIF))
+                {
+                    projectionDocument[fieldName] = json;
+                }
                 else
                 {
                     projectionDocument[fieldName] = "$" + json.ToString();

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

@@ -45,7 +45,7 @@ namespace SqlSugar.MongoDb
                         var funcString = context.ToString(model);
                         result = BsonDocument.Parse(funcString);
                     }
-                    else if (name.StartsWith("To"))
+                    else if (name.StartsWith("To")||name==nameof(SqlFunc.IIF))
                     {
                         var value = context.GetType().GetMethod(name).Invoke(context, new object[] { model });
                         result = BsonDocument.Parse(value?.ToString());

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

@@ -662,6 +662,20 @@ namespace SqlSugar.MongoDb
             return inDoc.ToJson(UtilMethods.GetJsonWriterSettings());
         }
 
+        public override string IIF(MethodCallExpressionModel model)
+        { 
+
+            var test = model.Args[0].MemberValue as Expression;
+            var ifTrue = model.Args[1].MemberValue as Expression;
+            var ifFalse = model.Args[2].MemberValue as Expression;
+
+            // 构造 ConditionalExpression
+            var conditionalExpr = Expression.Condition(test, ifTrue, ifFalse);
+
+            BsonValue testValue = new ConditionalExpressionTractor(context, null).Extract(conditionalExpr);
+            return testValue.ToJson(UtilMethods.GetJsonWriterSettings());
+        }
+
         #region  Helper 
         private static BsonValue GetMemberName(BsonValue memberName)
         {