[Navigate(NavigateType.OneToOne, nameof(SchoolId))]

public School School { get; set; } = new NavigationInitializer<School>();//support new

Src/Asp.NetCore2/SqlSugar/Abstract/QueryableProvider/NavigatManager.cs

@@ -392,6 +392,17 @@ namespace SqlSugar
                 FieldValue = String.Join(",", ids),
                 CSharpTypeName = navPkColumn?.UnderType?.Name
             }));
+            if (NavigationGlobalInstanceRegistry.IsAny()) 
+            {
+                foreach (var item in list)
+                {
+                    var firstObj = navObjectNamePropety.GetValue(item);
+                    if (NavigationGlobalInstanceRegistry.IsNavigationInitializerCreated(firstObj))
+                    {
+                        navObjectNamePropety.SetValue(item,null);
+                    }
+                }
+            }
             if (list.Any()&&navObjectNamePropety.GetValue(list.First()) == null)
             {
                 var sqlObj = GetWhereSql(db,navObjectNameColumnInfo.Navigat.Name);

Src/Asp.NetCore2/SqlSugar/Entities/NavigationInitializer.cs

@@ -0,0 +1,61 @@
+using System;
+using System.Collections.Generic;
+using System.Dynamic;
+using System.Reflection.Emit;
+using System.Reflection;
+using System.Text;
+
+namespace SqlSugar
+{
+    internal static class NavigationGlobalInstanceRegistry
+    {
+        private static readonly Dictionary<Type, object> _instances = new Dictionary<Type, object>();
+        private static readonly object _lock = new object();
+
+        public static Dictionary<Type, object> Instances => _instances;
+
+        public static bool IsAny() 
+        {
+            return _instances?.Count>0;
+        }
+        public static bool IsNavigationInitializerCreated(object instance)
+        {
+            if (instance == null)
+                return false;
+
+            Type type = instance.GetType();
+
+            lock (_lock)
+            {
+                return _instances.ContainsKey(type) && _instances[type] == instance;
+            }
+        }
+
+        public static void RegisterInstance(Type type, object instance)
+        {
+            lock (_lock)
+            {
+                if (!_instances.ContainsKey(type))
+                {
+                    _instances[type] = instance;
+                }
+            }
+        }
+    }
+
+    public class NavigationInitializer<T> where T : new()
+    {
+        public static implicit operator T(NavigationInitializer<T> initializer)
+        {
+            Type type = typeof(T);
+
+            if (!NavigationGlobalInstanceRegistry.Instances.ContainsKey(type))
+            {
+                T instance = new T();
+                NavigationGlobalInstanceRegistry.RegisterInstance(type, instance);
+            }
+
+            return (T)NavigationGlobalInstanceRegistry.Instances[type];
+        }
+    }
+}