diff --git a/c#/crawler/src/Db/CrawlerDbContext.cs b/c#/crawler/src/Db/CrawlerDbContext.cs
index a4bafab2..275a4875 100644
--- a/c#/crawler/src/Db/CrawlerDbContext.cs
+++ b/c#/crawler/src/Db/CrawlerDbContext.cs
@@ -30,13 +30,13 @@ public CrawlerDbContext() : this(fid: 0) { }
     public void TimestampingEntities() =>
 
         // https://www.entityframeworktutorial.net/faq/set-created-and-modified-date-in-efcore.aspx
-        ChangeTracker.Entries<ITimestampedEntity>().ForEach(e =>
+        ChangeTracker.Entries<TimestampedEntity>().ForEach(e =>
         {
             Helper.GetNowTimestamp(out var now);
             var originalEntityState = e.State; // copy e.State since it might change after any prop value updated
             var createdAtProp = e.Property(ie => ie.CreatedAt);
             var updatedAtProp = e.Property(ie => ie.UpdatedAt);
-            var lastSeenAtProp = e.Entity is IPost ? e.Property(ie => ((IPost)ie).LastSeenAt) : null;
+            var lastSeenAtProp = e.Entity is BasePost ? e.Property(ie => ((BasePost)ie).LastSeenAt) : null;
 
             // ReSharper disable once SwitchStatementMissingSomeEnumCasesNoDefault
             switch (originalEntityState)
diff --git a/c#/crawler/src/Db/Post/IPost.cs b/c#/crawler/src/Db/Post/BasePost.cs
similarity index 67%
rename from c#/crawler/src/Db/Post/IPost.cs
rename to c#/crawler/src/Db/Post/BasePost.cs
index 4304d173..91d7a3f0 100644
--- a/c#/crawler/src/Db/Post/IPost.cs
+++ b/c#/crawler/src/Db/Post/BasePost.cs
@@ -1,9 +1,10 @@
 // ReSharper disable UnusedMemberInSuper.Global
 namespace tbm.Crawler.Db.Post;
 
-public interface IPost : ITimestampedEntity, ICloneable
+public abstract class BasePost : TimestampedEntity, ICloneable
 {
     public ulong Tid { get; set; }
     public long AuthorUid { get; set; }
     public uint? LastSeenAt { get; set; }
+    public abstract object Clone();
 }
diff --git a/c#/crawler/src/Db/Post/IPostContent.cs b/c#/crawler/src/Db/Post/PostContent.cs
similarity index 60%
rename from c#/crawler/src/Db/Post/IPostContent.cs
rename to c#/crawler/src/Db/Post/PostContent.cs
index 45453793..4d56e7e6 100644
--- a/c#/crawler/src/Db/Post/IPostContent.cs
+++ b/c#/crawler/src/Db/Post/PostContent.cs
@@ -1,6 +1,6 @@
 namespace tbm.Crawler.Db.Post;
 
-public interface IPostContent
+public abstract class PostContent : RowVersionedEntity
 {
     public byte[]? ProtoBufBytes { get; set; }
 }
diff --git a/c#/crawler/src/Db/Post/IPostWithAuthorExpGrade.cs b/c#/crawler/src/Db/Post/PostWithAuthorExpGrade.cs
similarity index 71%
rename from c#/crawler/src/Db/Post/IPostWithAuthorExpGrade.cs
rename to c#/crawler/src/Db/Post/PostWithAuthorExpGrade.cs
index b266c3c1..9a4522db 100644
--- a/c#/crawler/src/Db/Post/IPostWithAuthorExpGrade.cs
+++ b/c#/crawler/src/Db/Post/PostWithAuthorExpGrade.cs
@@ -1,7 +1,7 @@
 // ReSharper disable UnusedMemberInSuper.Global
 namespace tbm.Crawler.Db.Post;
 
-public interface IPostWithAuthorExpGrade : IPost
+public abstract class PostWithAuthorExpGrade : BasePost
 {
     [NotMapped] public byte AuthorExpGrade { get; set; }
 }
diff --git a/c#/crawler/src/Db/Post/ReplyContent.cs b/c#/crawler/src/Db/Post/ReplyContent.cs
index 5f5ba136..e0f65fe3 100644
--- a/c#/crawler/src/Db/Post/ReplyContent.cs
+++ b/c#/crawler/src/Db/Post/ReplyContent.cs
@@ -1,8 +1,7 @@
 // ReSharper disable PropertyCanBeMadeInitOnly.Global
 namespace tbm.Crawler.Db.Post;
 
-public class ReplyContent : RowVersionedEntity, IPostContent
+public class ReplyContent : PostContent
 {
     [Key] public ulong Pid { get; set; }
-    public byte[]? ProtoBufBytes { get; set; }
 }
diff --git a/c#/crawler/src/Db/Post/ReplyPost.cs b/c#/crawler/src/Db/Post/ReplyPost.cs
index 873a372d..c2a40460 100644
--- a/c#/crawler/src/Db/Post/ReplyPost.cs
+++ b/c#/crawler/src/Db/Post/ReplyPost.cs
@@ -1,9 +1,8 @@
 // ReSharper disable PropertyCanBeMadeInitOnly.Global
 namespace tbm.Crawler.Db.Post;
 
-public class ReplyPost : RowVersionedEntity, IPostWithAuthorExpGrade
+public class ReplyPost : PostWithAuthorExpGrade
 {
-    public ulong Tid { get; set; }
     [Key] public ulong Pid { get; set; }
     public uint Floor { get; set; }
     [NotMapped] public byte[]? Content { get; set; }
@@ -11,8 +10,6 @@ public class ReplyPost : RowVersionedEntity, IPostWithAuthorExpGrade
     [JsonConverter(typeof(ProtoBufRepeatedFieldJsonConverter<Content>))]
     [NotMapped]
     public required RepeatedField<Content> OriginalContents { get; set; }
-    public long AuthorUid { get; set; }
-    [NotMapped] public byte AuthorExpGrade { get; set; }
     public uint? SubReplyCount { get; set; }
     public uint PostedAt { get; set; }
     public byte? IsFold { get; set; }
@@ -21,9 +18,6 @@ public class ReplyPost : RowVersionedEntity, IPostWithAuthorExpGrade
     public byte[]? Geolocation { get; set; }
     public uint? SignatureId { get; set; }
     [NotMapped] public byte[]? Signature { get; set; }
-    public uint CreatedAt { get; set; }
-    public uint? UpdatedAt { get; set; }
-    public uint? LastSeenAt { get; set; }
 
-    public object Clone() => MemberwiseClone();
+    public override object Clone() => MemberwiseClone();
 }
diff --git a/c#/crawler/src/Db/Post/SubReplyContent.cs b/c#/crawler/src/Db/Post/SubReplyContent.cs
index fec2c12a..3ebae1ff 100644
--- a/c#/crawler/src/Db/Post/SubReplyContent.cs
+++ b/c#/crawler/src/Db/Post/SubReplyContent.cs
@@ -1,8 +1,7 @@
 // ReSharper disable PropertyCanBeMadeInitOnly.Global
 namespace tbm.Crawler.Db.Post;
 
-public class SubReplyContent : RowVersionedEntity, IPostContent
+public class SubReplyContent : PostContent
 {
     [Key] public ulong Spid { get; set; }
-    public byte[]? ProtoBufBytes { get; set; }
 }
diff --git a/c#/crawler/src/Db/Post/SubReplyPost.cs b/c#/crawler/src/Db/Post/SubReplyPost.cs
index 65cc028c..5ee1d47d 100644
--- a/c#/crawler/src/Db/Post/SubReplyPost.cs
+++ b/c#/crawler/src/Db/Post/SubReplyPost.cs
@@ -1,9 +1,8 @@
 // ReSharper disable PropertyCanBeMadeInitOnly.Global
 namespace tbm.Crawler.Db.Post;
 
-public class SubReplyPost : RowVersionedEntity, IPostWithAuthorExpGrade
+public class SubReplyPost : PostWithAuthorExpGrade
 {
-    public ulong Tid { get; set; }
     public ulong Pid { get; set; }
     [Key] public ulong Spid { get; set; }
     [NotMapped] public byte[]? Content { get; set; }
@@ -11,14 +10,9 @@ public class SubReplyPost : RowVersionedEntity, IPostWithAuthorExpGrade
     [JsonConverter(typeof(ProtoBufRepeatedFieldJsonConverter<Content>))]
     [NotMapped]
     public required RepeatedField<Content> OriginalContents { get; set; }
-    public long AuthorUid { get; set; }
-    [NotMapped] public byte AuthorExpGrade { get; set; }
     public uint PostedAt { get; set; }
     public int? AgreeCount { get; set; }
     public int? DisagreeCount { get; set; }
-    public uint CreatedAt { get; set; }
-    public uint? UpdatedAt { get; set; }
-    public uint? LastSeenAt { get; set; }
 
-    public object Clone() => MemberwiseClone();
+    public override object Clone() => MemberwiseClone();
 }
diff --git a/c#/crawler/src/Db/Post/ThreadPost.cs b/c#/crawler/src/Db/Post/ThreadPost.cs
index 8d2919d5..6b66e86f 100644
--- a/c#/crawler/src/Db/Post/ThreadPost.cs
+++ b/c#/crawler/src/Db/Post/ThreadPost.cs
@@ -1,9 +1,9 @@
 // ReSharper disable PropertyCanBeMadeInitOnly.Global
 namespace tbm.Crawler.Db.Post;
 
-public class ThreadPost : RowVersionedEntity, IPost
+public class ThreadPost : BasePost
 {
-    [Key] public ulong Tid { get; set; }
+    [Key] public new ulong Tid { get; set; }
     [NotMapped] public ulong? FirstReplyPid { get; set; }
 
     [JsonConverter(typeof(ProtoBufRepeatedFieldJsonConverter<Abstract>))]
@@ -14,7 +14,6 @@ public class ThreadPost : RowVersionedEntity, IPost
     public string? TopicType { get; set; }
     public byte? IsGood { get; set; }
     public required string Title { get; set; }
-    public long AuthorUid { get; set; }
     public string? AuthorPhoneType { get; set; }
     public uint PostedAt { get; set; }
     public uint LatestReplyPostedAt { get; set; }
@@ -26,9 +25,6 @@ public class ThreadPost : RowVersionedEntity, IPost
     public int? DisagreeCount { get; set; }
     public byte[]? Zan { get; set; }
     public byte[]? Geolocation { get; set; }
-    public uint CreatedAt { get; set; }
-    public uint? UpdatedAt { get; set; }
-    public uint? LastSeenAt { get; set; }
 
-    public object Clone() => MemberwiseClone();
+    public override object Clone() => MemberwiseClone();
 }
diff --git a/c#/crawler/src/Db/Revision/AuthorRevision.cs b/c#/crawler/src/Db/Revision/AuthorRevision.cs
index afe957f3..2376a8ed 100644
--- a/c#/crawler/src/Db/Revision/AuthorRevision.cs
+++ b/c#/crawler/src/Db/Revision/AuthorRevision.cs
@@ -2,10 +2,8 @@
 // ReSharper disable UnusedAutoPropertyAccessor.Global
 namespace tbm.Crawler.Db.Revision;
 
-public abstract class AuthorRevision : RowVersionedEntity
+public abstract class AuthorRevision : ForumScopedRevision
 {
-    public uint DiscoveredAt { get; set; }
-    public uint Fid { get; set; }
     public long Uid { get; set; }
     public required PostType TriggeredBy { get; set; }
 }
diff --git a/c#/crawler/src/Db/Revision/ForumModeratorRevision.cs b/c#/crawler/src/Db/Revision/ForumModeratorRevision.cs
index 8f1c667f..fd0cfd83 100644
--- a/c#/crawler/src/Db/Revision/ForumModeratorRevision.cs
+++ b/c#/crawler/src/Db/Revision/ForumModeratorRevision.cs
@@ -1,10 +1,8 @@
 // ReSharper disable PropertyCanBeMadeInitOnly.Global
 namespace tbm.Crawler.Db.Revision;
 
-public class ForumModeratorRevision : RowVersionedEntity
+public class ForumModeratorRevision : ForumScopedRevision
 {
-    public uint DiscoveredAt { get; set; }
-    public uint Fid { get; set; }
     public required string Portrait { get; set; }
     public required string ModeratorTypes { get; set; }
 }
diff --git a/c#/crawler/src/Db/Revision/ForumScopedRevision.cs b/c#/crawler/src/Db/Revision/ForumScopedRevision.cs
new file mode 100644
index 00000000..29a13bb1
--- /dev/null
+++ b/c#/crawler/src/Db/Revision/ForumScopedRevision.cs
@@ -0,0 +1,7 @@
+namespace tbm.Crawler.Db.Revision;
+
+public abstract class ForumScopedRevision : RowVersionedEntity
+{
+    public uint DiscoveredAt { get; set; }
+    public uint Fid { get; set; }
+}
diff --git a/c#/crawler/src/Db/Revision/Splitting/IRevision.cs b/c#/crawler/src/Db/Revision/Splitting/BaseRevisionWithSplitting.cs
similarity index 59%
rename from c#/crawler/src/Db/Revision/Splitting/IRevision.cs
rename to c#/crawler/src/Db/Revision/Splitting/BaseRevisionWithSplitting.cs
index 53788ecd..3f0eb920 100644
--- a/c#/crawler/src/Db/Revision/Splitting/IRevision.cs
+++ b/c#/crawler/src/Db/Revision/Splitting/BaseRevisionWithSplitting.cs
@@ -1,9 +1,9 @@
 // ReSharper disable UnusedMemberInSuper.Global
 namespace tbm.Crawler.Db.Revision.Splitting;
 
-public interface IRevision
+public abstract class BaseRevisionWithSplitting : RowVersionedEntity
 {
     public uint TakenAt { get; set; }
     public ushort? NullFieldsBitMask { get; set; }
-    public bool IsAllFieldsIsNullExceptSplit();
+    public abstract bool IsAllFieldsIsNullExceptSplit();
 }
diff --git a/c#/crawler/src/Db/Revision/Splitting/RevisionWithSplitting.cs b/c#/crawler/src/Db/Revision/Splitting/RevisionWithSplitting.cs
index aad3345d..cd6c088c 100644
--- a/c#/crawler/src/Db/Revision/Splitting/RevisionWithSplitting.cs
+++ b/c#/crawler/src/Db/Revision/Splitting/RevisionWithSplitting.cs
@@ -1,15 +1,11 @@
 namespace tbm.Crawler.Db.Revision.Splitting;
 
-public abstract class RevisionWithSplitting<TBaseRevision> : RowVersionedEntity, IRevision
-    where TBaseRevision : class, IRevision
+public abstract class RevisionWithSplitting<TBaseRevision> : BaseRevisionWithSplitting
+    where TBaseRevision : BaseRevisionWithSplitting
 {
     private readonly Dictionary<Type, TBaseRevision> _splitEntities = [];
-
-    public uint TakenAt { get; set; }
-    public ushort? NullFieldsBitMask { get; set; }
     public IReadOnlyDictionary<Type, TBaseRevision> SplitEntities => _splitEntities;
-
-    public virtual bool IsAllFieldsIsNullExceptSplit() => throw new NotSupportedException();
+    public override bool IsAllFieldsIsNullExceptSplit() => throw new NotSupportedException();
 
     protected TValue? GetSplitEntityValue<TSplitEntity, TValue>
         (Func<TSplitEntity, TValue?> valueSelector)
diff --git a/c#/crawler/src/Db/ITimestampedEntity.cs b/c#/crawler/src/Db/TimestampedEntity.cs
similarity index 64%
rename from c#/crawler/src/Db/ITimestampedEntity.cs
rename to c#/crawler/src/Db/TimestampedEntity.cs
index 6a7e010a..da4cadb1 100644
--- a/c#/crawler/src/Db/ITimestampedEntity.cs
+++ b/c#/crawler/src/Db/TimestampedEntity.cs
@@ -1,6 +1,6 @@
 namespace tbm.Crawler.Db;
 
-public interface ITimestampedEntity
+public abstract class TimestampedEntity : RowVersionedEntity
 {
     public uint CreatedAt { get; set; }
     public uint? UpdatedAt { get; set; }
diff --git a/c#/crawler/src/Db/User.cs b/c#/crawler/src/Db/User.cs
index 23db5db1..5c9866f2 100644
--- a/c#/crawler/src/Db/User.cs
+++ b/c#/crawler/src/Db/User.cs
@@ -1,6 +1,6 @@
 namespace tbm.Crawler.Db;
 
-public class User : RowVersionedEntity, ITimestampedEntity
+public class User : TimestampedEntity
 {
     [Key] public long Uid { get; set; }
     public string? Name { get; set; }
@@ -11,8 +11,6 @@ public class User : RowVersionedEntity, ITimestampedEntity
     public string? FansNickname { get; set; }
     public byte[]? Icon { get; set; }
     public string? IpGeolocation { get; set; }
-    public uint CreatedAt { get; set; }
-    public uint? UpdatedAt { get; set; }
 
     public static User CreateLatestReplier(long uid, string? name, string? displayName) =>
         new() {Uid = uid, Name = name, DisplayName = displayName, Portrait = ""};
diff --git a/c#/crawler/src/Tieba/Crawl/Facade/BaseCrawlFacade.cs b/c#/crawler/src/Tieba/Crawl/Facade/BaseCrawlFacade.cs
index d50c3fb1..0edce0c5 100644
--- a/c#/crawler/src/Tieba/Crawl/Facade/BaseCrawlFacade.cs
+++ b/c#/crawler/src/Tieba/Crawl/Facade/BaseCrawlFacade.cs
@@ -12,8 +12,8 @@ public abstract class BaseCrawlFacade<TPost, TBaseRevision, TResponse, TPostProt
     Func<ConcurrentDictionary<Uid, User>, UserParser> userParserFactory,
     Func<ConcurrentDictionary<Uid, User>, UserSaver> userSaverFactory)
     : IDisposable
-    where TPost : class, IPost
-    where TBaseRevision : class, IRevision
+    where TPost : BasePost
+    where TBaseRevision : BaseRevisionWithSplitting
     where TResponse : class, IMessage<TResponse>
     where TPostProtoBuf : class, IMessage<TPostProtoBuf>
 {
diff --git a/c#/crawler/src/Tieba/Crawl/Parser/Post/BasePostParser.cs b/c#/crawler/src/Tieba/Crawl/Parser/Post/BasePostParser.cs
index f5621743..a69a125f 100644
--- a/c#/crawler/src/Tieba/Crawl/Parser/Post/BasePostParser.cs
+++ b/c#/crawler/src/Tieba/Crawl/Parser/Post/BasePostParser.cs
@@ -1,7 +1,7 @@
 namespace tbm.Crawler.Tieba.Crawl.Parser.Post;
 
 public abstract class BasePostParser<TPost, TPostProtoBuf>
-    where TPost : class, IPost
+    where TPost : BasePost
     where TPostProtoBuf : class, IMessage<TPostProtoBuf>
 {
     public void Parse(
@@ -18,7 +18,7 @@ public void Parse(
         outPosts = ParseInternal(inPosts, nullableUsers).ToDictionary(PostIdSelector, post => post);
         if (outPosts.Values.Any(p => p.AuthorUid == 0))
             throw new TiebaException(shouldRetry: true,
-                "Value of IPost.AuthorUid is the protoBuf default value 0.");
+                "Value of BasePost.AuthorUid is the protoBuf default value 0.");
 
         var users = new List<TbClient.User>(30);
         users.AddRange(nullableUsers.OfType<TbClient.User>()
diff --git a/c#/crawler/src/Tieba/Crawl/Saver/AuthorRevisionSaver.cs b/c#/crawler/src/Tieba/Crawl/Saver/AuthorRevisionSaver.cs
index 1a706215..df202930 100644
--- a/c#/crawler/src/Tieba/Crawl/Saver/AuthorRevisionSaver.cs
+++ b/c#/crawler/src/Tieba/Crawl/Saver/AuthorRevisionSaver.cs
@@ -13,7 +13,7 @@ public class AuthorRevisionSaver(PostType triggeredByPostType)
 
     public Action SaveAuthorExpGradeRevisions<TPostWithAuthorExpGrade>
         (CrawlerDbContext db, IReadOnlyCollection<TPostWithAuthorExpGrade> posts)
-        where TPostWithAuthorExpGrade : class, IPost, IPostWithAuthorExpGrade
+        where TPostWithAuthorExpGrade : PostWithAuthorExpGrade
     {
         SaveAuthorRevisions(db, posts, AuthorExpGradeLocks,
             db.AuthorExpGradeRevisions,
@@ -46,7 +46,7 @@ private void SaveAuthorRevisions<TPost, TRevision, TValue>(
         Func<TValue?, TValue?, bool> isValueChangedPredicate,
         Expression<Func<TRevision, LatestAuthorRevisionProjection<TValue>>> latestRevisionProjectionFactory,
         Func<(Uid Uid, TValue? Value, Time DiscoveredAt), TRevision> revisionFactory)
-        where TPost : class, IPost
+        where TPost : BasePost
         where TRevision : AuthorRevision
     {
         Helper.GetNowTimestamp(out var now);
diff --git a/c#/crawler/src/Tieba/Crawl/Saver/BaseSaver.cs b/c#/crawler/src/Tieba/Crawl/Saver/BaseSaver.cs
index 04fc4888..e81954f5 100644
--- a/c#/crawler/src/Tieba/Crawl/Saver/BaseSaver.cs
+++ b/c#/crawler/src/Tieba/Crawl/Saver/BaseSaver.cs
@@ -6,7 +6,7 @@ public abstract class BaseSaver<TBaseRevision>(ILogger<BaseSaver<TBaseRevision>>
 #pragma warning disable S1939 // Inheritance list should not be redundant
     : SaverWithRevision<TBaseRevision>, IFieldChangeIgnorance
 #pragma warning restore S1939 // Inheritance list should not be redundant
-    where TBaseRevision : class, IRevision
+    where TBaseRevision : BaseRevisionWithSplitting
 {
     protected void SavePostsOrUsers<TPostOrUser, TRevision>(
         CrawlerDbContext db,
@@ -15,7 +15,7 @@ protected void SavePostsOrUsers<TPostOrUser, TRevision>(
         ILookup<bool, TPostOrUser> existingOrNewLookup,
         Func<TPostOrUser, TPostOrUser> existingSelector)
         where TPostOrUser : class
-        where TRevision : class, IRevision
+        where TRevision : BaseRevisionWithSplitting
     {
         db.Set<TPostOrUser>().AddRange(existingOrNewLookup[false]); // newly added
         var newRevisions = existingOrNewLookup[true].Select(newPostOrUser =>
@@ -26,11 +26,11 @@ protected void SavePostsOrUsers<TPostOrUser, TRevision>(
             // this will mutate postOrUserInTracking which is referenced by entry
             entry.CurrentValues.SetValues(newPostOrUser);
 
-            bool IsTimestampingFieldName(string name) => name is nameof(IPost.LastSeenAt)
-                or nameof(ITimestampedEntity.CreatedAt) or nameof(ITimestampedEntity.UpdatedAt);
+            bool IsTimestampingFieldName(string name) => name is nameof(BasePost.LastSeenAt)
+                or nameof(TimestampedEntity.CreatedAt) or nameof(TimestampedEntity.UpdatedAt);
 
             // rollback changes that overwrite original values with the default value 0 or null
-            // for all fields of ITimestampedEntity and IPost.LastSeenAt
+            // for all fields of TimestampedEntity and BasePost.LastSeenAt
             // this will also affect the entity instance which postOrUserInTracking references to it
             entry.Properties
                 .Where(prop => prop.IsModified && IsTimestampingFieldName(prop.Metadata.Name))
diff --git a/c#/crawler/src/Tieba/Crawl/Saver/IFieldChangeIgnorance.cs b/c#/crawler/src/Tieba/Crawl/Saver/IFieldChangeIgnorance.cs
index d7e73216..d7fbfedc 100644
--- a/c#/crawler/src/Tieba/Crawl/Saver/IFieldChangeIgnorance.cs
+++ b/c#/crawler/src/Tieba/Crawl/Saver/IFieldChangeIgnorance.cs
@@ -71,7 +71,7 @@ when newValue is ""
                 && newValue is null && oldValue is not null) return true;
 
             // possible rarely respond with the protoBuf default value 0
-            return propName == nameof(IPost.AuthorUid)
+            return propName == nameof(BasePost.AuthorUid)
                    && newValue is 0L && oldValue is not null;
         },
         Revision: (whichPostType, propName, oldValue, _) =>
diff --git a/c#/crawler/src/Tieba/Crawl/Saver/Post/BasePostSaver.cs b/c#/crawler/src/Tieba/Crawl/Saver/Post/BasePostSaver.cs
index 3af394b9..40537786 100644
--- a/c#/crawler/src/Tieba/Crawl/Saver/Post/BasePostSaver.cs
+++ b/c#/crawler/src/Tieba/Crawl/Saver/Post/BasePostSaver.cs
@@ -8,8 +8,8 @@ public abstract class BasePostSaver<TPost, TBaseRevision>(
         AuthorRevisionSaver.New authorRevisionSaverFactory,
         PostType currentPostType)
     : BaseSaver<TBaseRevision>(logger)
-    where TPost : class, IPost
-    where TBaseRevision : class, IRevision
+    where TPost : BasePost
+    where TBaseRevision : BaseRevisionWithSplitting
 {
     protected delegate void PostSaveEventHandler();
     [SuppressMessage("Design", "MA0046:Use EventHandler<T> to declare events")]
@@ -30,7 +30,7 @@ protected SaverChangeSet<TPost> Save<TRevision>(
         Func<TPost, PostId> postIdSelector,
         Func<TPost, TRevision> revisionFactory,
         ExpressionStarter<TPost> existingPostPredicate)
-        where TRevision : class, IRevision
+        where TRevision : BaseRevisionWithSplitting
     {
         var existingPostsKeyById = db.Set<TPost>()
             .Where(existingPostPredicate).ToDictionary(postIdSelector);
diff --git a/c#/crawler/src/Tieba/Crawl/Saver/SaverChangeSet.cs b/c#/crawler/src/Tieba/Crawl/Saver/SaverChangeSet.cs
index fd826909..59fb8def 100644
--- a/c#/crawler/src/Tieba/Crawl/Saver/SaverChangeSet.cs
+++ b/c#/crawler/src/Tieba/Crawl/Saver/SaverChangeSet.cs
@@ -4,7 +4,7 @@ public class SaverChangeSet<TPost>(
     IReadOnlyCollection<TPost> existingBefore,
     ICollection<TPost> existingAfterAndNewlyAdded,
     Func<TPost, PostId> postIdSelector)
-    where TPost : class, IPost
+    where TPost : BasePost
 {
     public IReadOnlyCollection<(TPost Before, TPost After)> Existing { get; } = existingBefore
         .OrderBy(postIdSelector)
diff --git a/c#/crawler/src/Tieba/Crawl/Saver/SaverWithRevision.cs b/c#/crawler/src/Tieba/Crawl/Saver/SaverWithRevision.cs
index c1bf5f67..78336ea5 100644
--- a/c#/crawler/src/Tieba/Crawl/Saver/SaverWithRevision.cs
+++ b/c#/crawler/src/Tieba/Crawl/Saver/SaverWithRevision.cs
@@ -1,7 +1,7 @@
 namespace tbm.Crawler.Tieba.Crawl.Saver;
 
 public abstract class SaverWithRevision<TBaseRevision> : IRevisionProperties
-    where TBaseRevision : class, IRevision
+    where TBaseRevision : BaseRevisionWithSplitting
 {
     protected delegate void RevisionUpsertDelegate(CrawlerDbContext db, IEnumerable<TBaseRevision> revision);
 
diff --git a/c#/imagePipeline/src/Consumer/MetadataConsumer.cs b/c#/imagePipeline/src/Consumer/MetadataConsumer.cs
index 24dbada4..f500c4d7 100644
--- a/c#/imagePipeline/src/Consumer/MetadataConsumer.cs
+++ b/c#/imagePipeline/src/Consumer/MetadataConsumer.cs
@@ -94,7 +94,7 @@ private Func<ImageWithBytes, ImageMetadata> GetImageMetaData
         TImageSharpProfile? profile,
         Func<TImageSharpProfile, byte[]?> rawBytesSelector)
         where TImageSharpProfile : class
-        where TEmbeddedMetadata : class, ImageMetadata.IEmbedded, new()
+        where TEmbeddedMetadata : ImageMetadata.Embedded, new()
     {
         if (profile == null) return null;
         var rawBytes = rawBytesSelector(profile); // will be null when param profile is null
diff --git a/c#/imagePipeline/src/Db/ImageFailed.cs b/c#/imagePipeline/src/Db/ImageFailed.cs
index b0ca9020..423238af 100644
--- a/c#/imagePipeline/src/Db/ImageFailed.cs
+++ b/c#/imagePipeline/src/Db/ImageFailed.cs
@@ -3,10 +3,9 @@
 
 namespace tbm.ImagePipeline.Db;
 
-public class ImageFailed : RowVersionedEntity
+public class ImageFailed : EntityWithImageId
 {
     [Key] [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
     public uint Id { get; set; }
-    public uint ImageId { get; set; }
     public required string Exception { get; set; }
 }
diff --git a/c#/imagePipeline/src/Db/ImageHash.cs b/c#/imagePipeline/src/Db/ImageHash.cs
index d4eb672d..882222b7 100644
--- a/c#/imagePipeline/src/Db/ImageHash.cs
+++ b/c#/imagePipeline/src/Db/ImageHash.cs
@@ -1,10 +1,8 @@
 // ReSharper disable PropertyCanBeMadeInitOnly.Global
 namespace tbm.ImagePipeline.Db;
 
-public class ImageHash : RowVersionedEntity
+public class ImageHash : ImageWithFrameIndex
 {
-    public uint ImageId { get; set; }
-    public uint FrameIndex { get; set; }
     public required byte[] PHash { get; set; }
     public required byte[] AverageHash { get; set; }
     public required byte[] BlockMeanHash { get; set; }
diff --git a/c#/imagePipeline/src/Db/ImageMetadata.cs b/c#/imagePipeline/src/Db/ImageMetadata.cs
index 815aeedb..2ce13f30 100644
--- a/c#/imagePipeline/src/Db/ImageMetadata.cs
+++ b/c#/imagePipeline/src/Db/ImageMetadata.cs
@@ -5,23 +5,12 @@
 using System.ComponentModel;
 using SixLabors.ImageSharp.PixelFormats;
 using Point = NetTopologySuite.Geometries.Point;
+using EntityWithImageIdAsKey = tbm.Shared.Db.EntityWithImageId.AsKey;
 
 namespace tbm.ImagePipeline.Db;
 
-public class ImageMetadata : RowVersionedEntity, ImageMetadata.IImageMetadata
+public class ImageMetadata : EntityWithImageIdAsKey
 {
-    public interface IImageMetadata
-    {
-        [Key] public uint ImageId { get; set; }
-    }
-
-    public interface IEmbedded : IImageMetadata
-    {
-        public byte[] XxHash3 { get; set; }
-        public byte[]? RawBytes { get; set; }
-    }
-
-    [Key] public uint ImageId { get; set; }
     public string? Format { get; set; }
     public ushort Width { get; set; }
     public ushort Height { get; set; }
@@ -40,14 +29,19 @@ public interface IEmbedded : IImageMetadata
     public Gif? GifMetadata { get; set; }
     public Bmp? BmpMetadata { get; set; }
 
-    public class ByteSize : RowVersionedEntity, IImageMetadata
+    public class ByteSize : EntityWithImageIdAsKey
     {
-        [Key] public uint ImageId { get; set; }
         [SuppressMessage("Naming", "AV1710:Member name includes the name of its containing type")]
         public uint DownloadedByteSize { get; set; }
     }
 
-    public class Exif : RowVersionedEntity, IEmbedded
+    public abstract class Embedded : EntityWithImageIdAsKey
+    {
+        public byte[] XxHash3 { get; set; } = null!;
+        public byte[]? RawBytes { get; set; }
+    }
+
+    public class Exif : Embedded
     {
         [SuppressMessage("ApiDesign", "SS039:An enum should specify a default value")]
         public enum ExifOrientation
@@ -62,7 +56,6 @@ public enum ExifOrientation
             Rotate270Cw = 8
         }
 
-        [Key] public uint ImageId { get; set; }
         public string? Orientation { get; set; }
         public string? ImageDescription { get; set; }
         public string? UserComment { get; set; }
@@ -88,44 +81,23 @@ public enum ExifOrientation
         public Point? GpsCoordinate { get; set; }
         public float? GpsImgDirection { get; set; }
         public string? GpsImgDirectionRef { get; set; }
-        public byte[] XxHash3 { get; set; } = null!;
-        public byte[]? RawBytes { get; set; }
 
         // workaround to work with MetadataConsumer.CreateEmbeddedFromProfile()
         // https://stackoverflow.com/questions/75266722/type-cannot-satisfy-the-new-constraint-on-parameter-tparam-because-type
         public IEnumerable<TagName> TagNames { get; set; } = [];
 
-        public class TagName : RowVersionedEntity, IImageMetadata
+        public class TagName : EntityWithImageId
         {
-            public uint ImageId { get; set; }
             public required string Name { get; set; }
         }
     }
 
-    public class Icc : RowVersionedEntity, IEmbedded
-    {
-        [Key] public uint ImageId { get; set; }
-        public byte[] XxHash3 { get; set; } = null!;
-        public byte[]? RawBytes { get; set; }
-    }
-
-    public class Iptc : RowVersionedEntity, IEmbedded
-    {
-        [Key] public uint ImageId { get; set; }
-        public byte[] XxHash3 { get; set; } = null!;
-        public byte[]? RawBytes { get; set; }
-    }
-
-    public class Xmp : RowVersionedEntity, IEmbedded
-    {
-        [Key] public uint ImageId { get; set; }
-        public byte[] XxHash3 { get; set; } = null!;
-        public byte[]? RawBytes { get; set; }
-    }
+    public class Icc : Embedded;
+    public class Iptc : Embedded;
+    public class Xmp : Embedded;
 
-    public class Jpg : RowVersionedEntity, IImageMetadata
+    public class Jpg : EntityWithImageIdAsKey
     {
-        [Key] public uint ImageId { get; set; }
         public int Quality { get; set; }
         public string? ColorType { get; set; }
         public bool? Interleaved { get; set; }
@@ -145,9 +117,8 @@ public class Jpg : RowVersionedEntity, IImageMetadata
         }
     }
 
-    public class Png : RowVersionedEntity, IImageMetadata
+    public class Png : EntityWithImageIdAsKey
     {
-        [Key] public uint ImageId { get; set; }
         public string? BitDepth { get; set; }
         public string? ColorType { get; set; }
         public string? InterlaceMethod { get; set; }
@@ -178,9 +149,8 @@ public class Png : RowVersionedEntity, IImageMetadata
         }
     }
 
-    public class Gif : RowVersionedEntity, IImageMetadata
+    public class Gif : EntityWithImageIdAsKey
     {
-        [Key] public uint ImageId { get; set; }
         public ushort RepeatCount { get; set; }
         public required string ColorTableMode { get; set; }
         public int GlobalColorTableLength { get; set; }
@@ -203,9 +173,8 @@ public class Gif : RowVersionedEntity, IImageMetadata
         }
     }
 
-    public class Bmp : RowVersionedEntity, IImageMetadata
+    public class Bmp : EntityWithImageIdAsKey
     {
-        [Key] public uint ImageId { get; set; }
         public required string InfoHeaderType { get; set; }
         public required string BitsPerPixel { get; set; }
 
diff --git a/c#/imagePipeline/src/Db/ImageOcrBox.cs b/c#/imagePipeline/src/Db/ImageOcrBox.cs
index da8a0e03..cd89d240 100644
--- a/c#/imagePipeline/src/Db/ImageOcrBox.cs
+++ b/c#/imagePipeline/src/Db/ImageOcrBox.cs
@@ -1,10 +1,8 @@
 // ReSharper disable PropertyCanBeMadeInitOnly.Global
 namespace tbm.ImagePipeline.Db;
 
-public class ImageOcrBox : RowVersionedEntity
+public class ImageOcrBox : ImageWithFrameIndex
 {
-    public uint ImageId { get; set; }
-    public uint FrameIndex { get; set; }
     public ushort CenterPointX { get; set; }
     public ushort CenterPointY { get; set; }
     public ushort Width { get; set; }
diff --git a/c#/imagePipeline/src/Db/ImageOcrLine.cs b/c#/imagePipeline/src/Db/ImageOcrLine.cs
index 5af886eb..5cb6d9b6 100644
--- a/c#/imagePipeline/src/Db/ImageOcrLine.cs
+++ b/c#/imagePipeline/src/Db/ImageOcrLine.cs
@@ -1,9 +1,7 @@
 // ReSharper disable PropertyCanBeMadeInitOnly.Global
 namespace tbm.ImagePipeline.Db;
 
-public class ImageOcrLine : RowVersionedEntity
+public class ImageOcrLine : ImageWithFrameIndex
 {
-    public uint ImageId { get; set; }
-    public uint FrameIndex { get; set; }
     public required string TextLines { get; set; }
 }
diff --git a/c#/imagePipeline/src/Db/ImagePipelineDbContext.cs b/c#/imagePipeline/src/Db/ImagePipelineDbContext.cs
index 2f9697dc..c5cded19 100644
--- a/c#/imagePipeline/src/Db/ImagePipelineDbContext.cs
+++ b/c#/imagePipeline/src/Db/ImagePipelineDbContext.cs
@@ -41,7 +41,7 @@ protected override void OnModelCreating(ModelBuilder b)
 
         void SplitImageMetadata<TRelatedEntity>
             (Expression<Func<ImageMetadata, TRelatedEntity?>> keySelector, string tableNameSuffix)
-            where TRelatedEntity : class, IImageMetadata
+            where TRelatedEntity : EntityWithImageId
         {
             b.Entity<ImageMetadata>().HasOne(keySelector).WithOne().HasForeignKey<TRelatedEntity>(e => e.ImageId);
             b.Entity<TRelatedEntity>().ToTable($"tbmi_metadata_{tableNameSuffix}");
diff --git a/c#/imagePipeline/src/Db/ImageQrCode.cs b/c#/imagePipeline/src/Db/ImageQrCode.cs
index 38a7a96c..1dae698f 100644
--- a/c#/imagePipeline/src/Db/ImageQrCode.cs
+++ b/c#/imagePipeline/src/Db/ImageQrCode.cs
@@ -1,10 +1,8 @@
 // ReSharper disable PropertyCanBeMadeInitOnly.Global
 namespace tbm.ImagePipeline.Db;
 
-public class ImageQrCode : RowVersionedEntity
+public class ImageQrCode : ImageWithFrameIndex
 {
-    public uint ImageId { get; set; }
-    public uint FrameIndex { get; set; }
     public short Point1X { get; set; }
     public short Point1Y { get; set; }
     public short Point2X { get; set; }
diff --git a/c#/imagePipeline/src/Db/ImageWithFrameIndex.cs b/c#/imagePipeline/src/Db/ImageWithFrameIndex.cs
new file mode 100644
index 00000000..61ebf29b
--- /dev/null
+++ b/c#/imagePipeline/src/Db/ImageWithFrameIndex.cs
@@ -0,0 +1,6 @@
+namespace tbm.ImagePipeline.Db;
+
+public abstract class ImageWithFrameIndex : EntityWithImageId
+{
+    public uint FrameIndex { get; set; }
+}
diff --git a/c#/shared/src/Db/EntitiesWithImageId.cs b/c#/shared/src/Db/EntitiesWithImageId.cs
new file mode 100644
index 00000000..b3f0c3cb
--- /dev/null
+++ b/c#/shared/src/Db/EntitiesWithImageId.cs
@@ -0,0 +1,13 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace tbm.Shared.Db;
+
+public abstract class EntityWithImageId : RowVersionedEntity
+{
+    public uint ImageId { get; set; }
+
+    public abstract class AsKey : EntityWithImageId
+    {
+        [Key] public new uint ImageId { get; set; }
+    }
+}
diff --git a/c#/shared/src/Db/ImageInReply.cs b/c#/shared/src/Db/ImageInReply.cs
index 44074577..d2bb7934 100644
--- a/c#/shared/src/Db/ImageInReply.cs
+++ b/c#/shared/src/Db/ImageInReply.cs
@@ -1,11 +1,8 @@
 // ReSharper disable PropertyCanBeMadeInitOnly.Global
-using System.ComponentModel.DataAnnotations;
-
 namespace tbm.Shared.Db;
 
-public class ImageInReply : RowVersionedEntity
+public class ImageInReply : EntityWithImageId.AsKey
 {
-    [Key] public uint ImageId { get; set; }
     public required string UrlFilename { get; set; }
     public uint ExpectedByteSize { get; set; }
     public bool MetadataConsumed { get; set; }
diff --git a/c#/shared/src/Db/ReplyContentImage.cs b/c#/shared/src/Db/ReplyContentImage.cs
index a84e0ac4..6892fde8 100644
--- a/c#/shared/src/Db/ReplyContentImage.cs
+++ b/c#/shared/src/Db/ReplyContentImage.cs
@@ -1,9 +1,8 @@
 // ReSharper disable PropertyCanBeMadeInitOnly.Global
 namespace tbm.Shared.Db;
 
-public class ReplyContentImage
+public class ReplyContentImage : EntityWithImageId
 {
     public ulong Pid { get; set; }
-    public uint ImageId { get; set; }
     public required ImageInReply ImageInReply { get; set; }
 }