Add deserialization hook to bsonmapper

Author: JKamsker

LiteDB.Tests/Database/DocumentUpgrade_Tests.cs

@@ -1,4 +1,4 @@
-using FluentAssertions;
+using FluentAssertions;
 
 using LiteDB.Engine;
 
@@ -38,10 +38,24 @@ public void DocumentUpgrade_Test()
 
         ms.Position = 0;
 
-        var engine = new LiteEngine(new EngineSettings
+        using var engine = new LiteEngine(new EngineSettings
         {
             DataStream = ms,
-            ReadTransform = ReadTransform
+            ReadTransform = (collectionName, val) =>
+            {
+                if (val is not BsonDocument doc)
+                {
+                    return val;
+                }
+
+                if (doc.TryGetValue("version", out var version) && version.AsInt32 == 1)
+                {
+                    doc["version"] = 2;
+                    doc["age"] = 30;
+                }
+
+                return val;
+            }
         });
 
         using (var db = new LiteDatabase(engine))
@@ -58,19 +72,62 @@ public void DocumentUpgrade_Test()
         }
     }
 
-    private BsonValue ReadTransform(string arg1, BsonValue val)
+    [Fact]
+    public void DocumentUpgrade_BsonMapper_Test()
     {
-        if (!(val is BsonDocument bdoc))
+        var ms = new MemoryStream();
+        using (var db = new LiteDatabase(ms))
         {
-            return val;
+            var col = db.GetCollection("col");
+
+            col.Insert(new BsonDocument { ["version"] = 1, ["_id"] = 1, ["name"] = "John" });
         }
 
-        if (bdoc.TryGetValue("version", out var version) && version.AsInt32 == 1)
+        ms.Position = 0;
+
+        using (var db = new LiteDatabase(ms))
         {
-            bdoc["version"] = 2;
-            bdoc["age"] = 30;
+            var col = db.GetCollection("col");
+
+            col.Count().Should().Be(1);
+
+            var doc = col.FindById(1);
+
+            doc["version"].AsInt32.Should().Be(1);
+            doc["name"].AsString.Should().Be("John");
+            doc["age"].AsInt32.Should().Be(0);
         }
 
-        return val;
+        ms.Position = 0;
+
+        var mapper = new BsonMapper();
+        mapper.OnDeserialization = (sender, type, val) =>
+        {
+            if (val is not BsonDocument doc)
+            {
+                return val;
+            }
+
+            if (doc.TryGetValue("version", out var version) && version.AsInt32 == 1)
+            {
+                doc["version"] = 2;
+                doc["age"] = 30;
+            }
+
+            return doc;
+        };
+
+        using (var db = new LiteDatabase(ms, mapper))
+        {
+            var col = db.GetCollection("col");
+
+            col.Count().Should().Be(1);
+
+            var doc = col.FindById(1);
+
+            doc["version"].AsInt32.Should().Be(2);
+            doc["name"].AsString.Should().Be("John");
+            doc["age"].AsInt32.Should().Be(30);
+        }
     }
 }

LiteDB/Client/Mapper/BsonMapper.Deserialize.cs

@@ -9,6 +9,24 @@ namespace LiteDB
 {
     public partial class BsonMapper
     {
+        #region Deserialization Hooks
+
+        /// <summary>
+        /// Delegate for deserialization callback.
+        /// </summary>
+        /// <param name="sender">The BsonMapper instance that triggered the deserialization.</param>
+        /// <param name="target">The target type for deserialization.</param>
+        /// <param name="value">The BsonValue to be deserialized.</param>
+        /// <returns>The deserialized BsonValue.</returns>
+        public delegate BsonValue DeserializationCallback(BsonMapper sender, Type target, BsonValue value);
+
+        /// <summary>
+        /// Gets called before deserialization of a value
+        /// </summary>
+        public DeserializationCallback? OnDeserialization { get; set; }
+
+        #endregion Deserialization Hooks
+
         #region Basic direct .NET convert types
 
         // direct bson types
@@ -78,6 +96,15 @@ public T Deserialize<T>(BsonValue value)
         /// </summary>
         public object Deserialize(Type type, BsonValue value)
         {
+            if (OnDeserialization is not null)
+            {
+                var result = OnDeserialization(this, type, value);
+                if (result is not null)
+                {
+                    value = result;
+                }
+            }
+
             // null value - null returns
             if (value.IsNull) return null;
 

LiteDB/LiteDB.csproj

@@ -28,6 +28,7 @@
     <SignAssembly Condition="'$(OS)'=='Windows_NT'">true</SignAssembly>
     <AssemblyOriginatorKeyFile Condition="'$(Configuration)' == 'Release'">LiteDB.snk</AssemblyOriginatorKeyFile>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+	<LangVersion>9.0</LangVersion>
   </PropertyGroup>
 
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