Change compiler to C# 4 to be compatible with UnitÂ3D

Database/LiteDatabase.cs

@@ -187,7 +187,7 @@ public bool RenameCollection(string oldName, string newName)
         /// </summary>
         public long Shrink()
         {
-            return this.Shrink(_connectionString?.Password);
+            return this.Shrink(_connectionString == null ? null : _connectionString.Password);
         }
 
         /// <summary>

Engine/Pages/ExtendPage.cs

@@ -16,7 +16,7 @@ internal class ExtendPage : BasePage
         /// <summary>
         /// Represent the part or full of the object - if this page has NextPageID the object is bigger than this page
         /// </summary>
-        public Byte[] Data { get; set; }
+        public byte[] Data { get; set; }
 
         public ExtendPage(uint pageID)
             : base(pageID)

Engine/Pages/HeaderPage.cs

@@ -22,6 +22,7 @@ internal class HeaderPage : BasePage
 
         /// <summary>
         /// Get/Set the pageID that start sequenece with a complete empty pages (can be used as a new page)
+        /// Must be a field to be used as "ref"
         /// </summary>
         public uint FreeEmptyPageID;
 
@@ -33,17 +34,17 @@ internal class HeaderPage : BasePage
         /// <summary>
         /// Database user version [2 bytes]
         /// </summary>
-        public ushort UserVersion = 0;
+        public ushort UserVersion { get; set; }
 
         /// <summary>
         /// Password hash in SHA1 [20 bytes]
         /// </summary>
-        public byte[] Password = new byte[20];
+        public byte[] Password { get; set; }
 
         /// <summary>
         /// When using encryption, store salt for password
         /// </summary>
-        public byte[] Salt = new byte[16];
+        public byte[] Salt { get; set; }
 
         /// <summary>
         /// Get a dictionary with all collection pages with pageID link

Engine/Update/IDatafileUpdate.cs

@@ -0,0 +1,17 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Text;
+
+namespace LiteDB
+{
+    interface IDatafileUpdate
+    {
+        bool IsFileVersion(Stream stream);
+        void Initialize(Stream stream);
+        IEnumerable<string> ReadCollections();
+        IEnumerable<KeyValuePair<string, bool>> ReadIndexes(string colName);
+        IEnumerable<BsonDocument> ReadDocuments(string colName);
+    }
+}

Engine/Update/V6/DbReader.cs

@@ -0,0 +1,145 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+
+namespace LiteDB.Update.V6
+{
+    internal class DbReader
+    {
+        private const int PAGE_SIZE = 4096;
+
+        private Stream _stream;
+
+
+        #region DiskService
+
+        /// <summary>
+        /// Read page bytes from disk and convert to Page object
+        /// </summary>
+        private T ReadPageDisk<T>(uint pageID)
+            where T : BasePage_v6
+        {
+            // position cursor in stream
+            _stream.Seek(pageID * (uint)PAGE_SIZE, SeekOrigin.Begin);
+
+            var buffer = new byte[PAGE_SIZE];
+
+            // read bytes from stream
+            _stream.Read(buffer, 0, BasePage.PAGE_SIZE);
+
+            var reader = new ByteReader(buffer);
+
+            // page header
+            reader.ReadUInt32(); // read PageID
+            var pageType = (PageType)reader.ReadByte();
+            var prevPageID = reader.ReadUInt32();
+            var nextPageID = reader.ReadUInt32();
+            var itemCount = reader.ReadUInt16();
+            reader.ReadUInt16(); // FreeBytes
+            reader.Skip(8); // reserved 8 bytes
+
+            T page;
+
+            switch (pageType)
+            {
+                case PageType.Header: page = this.ReadHeaderPage(reader) as T; break;
+                case PageType.Collection: page = this.ReadCollectionPage(reader) as T; break;
+                //case PageType.Index: return new IndexPage(pageID);
+                //case PageType.Data: return new DataPage(pageID);
+                //case PageType.Extend: return new ExtendPage(pageID);
+                //case PageType.Empty: return new EmptyPage(pageID);
+                default: throw new Exception("Invalid pageType");
+            }
+
+            // setting page header 
+            page.PageID = pageID;
+            page.PageType = pageType;
+            page.PrevPageID = prevPageID;
+            page.NextPageID = nextPageID;
+            page.ItemCount = itemCount;
+
+            return page;
+        }
+
+        /// <summary>
+        /// Read Header page from ByteReader
+        /// </summary>
+        private HeaderPage_v6 ReadHeaderPage(ByteReader reader)
+        {
+            var page = new HeaderPage_v6();
+
+            reader.Skip(100);
+
+            var cols = reader.ReadByte();
+            for (var i = 0; i < cols; i++)
+            {
+                page.CollectionPages.Add(reader.ReadString(), reader.ReadUInt32());
+            }
+
+            return page;
+        }
+
+        /// <summary>
+        /// Read Collection page from ByteReader
+        /// </summary>
+        private CollectionPage_v6 ReadCollectionPage(ByteReader reader)
+        {
+            var page = new CollectionPage_v6();
+
+            page.CollectionName = reader.ReadString();
+            page.DocumentCount = reader.ReadInt64();
+            reader.ReadUInt32(); // FreeDataPageID
+
+            page.Indexes = new Dictionary<string, bool>();
+
+
+            return page;
+        }
+
+        #endregion
+
+        #region PagerService
+
+        private Dictionary<uint, BasePage_v6> _cache = new Dictionary<uint, BasePage_v6>();
+
+        /// <summary>
+        /// Read a page from cache or from disk. If cache exceed 5000 pages, clear cache
+        /// </summary>
+        private T GetPage<T>(uint pageID)
+            where T : BasePage_v6
+        {
+            BasePage_v6 page;
+
+            if(_cache.Count > 5000) _cache.Clear();
+
+            if(_cache.TryGetValue(pageID, out page))
+            {
+                return (T)page;
+            }
+
+            page = _cache[pageID] = this.ReadPageDisk<T>(pageID);
+
+            return (T)page;
+        }
+
+        /// <summary>
+        /// Get all pages in sequence using NextPageID
+        /// </summary>
+        private IEnumerable<T> GetSeqPages<T>(uint firstPageID)
+            where T : BasePage_v6
+        {
+            var pageID = firstPageID;
+
+            while (pageID != uint.MaxValue)
+            {
+                var page = this.GetPage<T>(pageID);
+
+                pageID = page.NextPageID;
+
+                yield return page;
+            }
+        }
+
+        #endregion
+    }
+}

Engine/Update/V6/Pages.cs

@@ -0,0 +1,61 @@
+using System;
+using System.Collections.Generic;
+
+namespace LiteDB.Update.V6
+{
+    internal class BasePage_v6
+    {
+        public uint PageID { get; set; }
+        public PageType PageType { get; set; }
+        public uint PrevPageID { get; set; }
+        public uint NextPageID { get; set; }
+        public int ItemCount { get; set; }
+    }
+
+    internal class HeaderPage_v6 : BasePage_v6
+    {
+        public byte[] Password { get; set; }
+        public Dictionary<string, uint> CollectionPages { get; set; }
+    }
+
+    internal class CollectionPage_v6 : BasePage_v6
+    {
+        public string CollectionName { get; set; }
+        public long DocumentCount { get; set; }
+        public PageAddress HeaderNode { get; set; }
+        public Dictionary<string, bool> Indexes { get; set; }
+    }
+
+    internal class IndexPage_v6 : BasePage_v6
+    {
+        public Dictionary<ushort, IndexNode_v6> Nodes { get; set; }
+    }
+
+    internal class DataPage_v6 : BasePage_v6
+    {
+        public Dictionary<ushort, DataBlock_v6> DataBlocks { get; set; }
+    }
+
+    internal class ExtendPage_v6 : BasePage_v6
+    {
+        public byte[] Data { get; set; }
+    }
+
+    internal class DataBlock_v6
+    {
+        public PageAddress Position { get; set; }
+        public PageAddress[] IndexRef { get; set; }
+        public uint ExtendPageID { get; set; }
+        public byte[] Data { get; set; }
+    }
+
+    internal class IndexNode_v6
+    {
+        public PageAddress Position { get; set; }
+        public PageAddress[] Prev { get; set; }
+        public PageAddress[] Next { get; set; }
+        public ushort KeyLength { get; set; }
+        public BsonValue Key { get; set; }
+        public PageAddress DataBlock { get; set; }
+    }
+}

LiteDB.NetStandard.csproj

@@ -151,6 +151,7 @@
     <Compile Include="Utils\Extensions\StreamExtensions.cs" />
     <Compile Include="Utils\Extensions\StringExtensions.cs" />
     <Compile Include="Utils\Extensions\TypeExtensions.cs" />
+    <Compile Include="Utils\FileHelper.cs" />
     <Compile Include="Utils\FileOptions.cs" />
     <Compile Include="Utils\IndexNotFoundException.cs" />
     <Compile Include="Utils\LazyLoad.cs" />

LiteDB.csproj

@@ -26,6 +26,7 @@
     <NoWarn>1591</NoWarn>
     <Prefer32Bit>false</Prefer32Bit>
     <PlatformTarget>AnyCPU</PlatformTarget>
+    <LangVersion>4</LangVersion>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
     <DebugType>pdbonly</DebugType>
@@ -57,6 +58,7 @@
     <Compile Include="Database\Collections\Include.cs" />
     <Compile Include="Database\Collections\Index.cs" />
     <Compile Include="Database\Collections\Insert.cs" />
+    <Compile Include="Database\Collections\Upsert.cs" />
     <Compile Include="Database\Collections\Update.cs" />
     <Compile Include="Database\Collections\LiteCollection.cs" />
     <Compile Include="Database\LiteDatabase.cs" />
@@ -107,6 +109,7 @@
     <Compile Include="Engine\Structures\IndexNode.cs" />
     <Compile Include="Engine\Structures\IndexInfo.cs" />
     <Compile Include="Mapper\Attributes\BsonRefAttribute.cs" />
+    <Compile Include="Utils\FileHelper.cs" />
     <Compile Include="Utils\LiteTransaction.cs" />
     <Compile Include="Engine\Structures\PageAddress.cs" />
     <Compile Include="Mapper\Attributes\BsonFieldAttribute.cs" />

Mapper/BsonMapper.cs

@@ -331,10 +331,9 @@ protected virtual EntityMapper BuildEntityMapper(Type type)
                 var index = (BsonIndexAttribute)memberInfo.GetCustomAttributes(indexAttr, false).FirstOrDefault();
 
                 // get data type
-                var dataType = 
-                    (memberInfo as PropertyInfo)?.PropertyType ??
-                    (memberInfo as FieldInfo)?.FieldType ??
-                    typeof(object);
+                var dataType = memberInfo is PropertyInfo ?
+                    (memberInfo as PropertyInfo).PropertyType :
+                    (memberInfo as FieldInfo).FieldType;
 
                 // check if datatype is list/array
                 var isList = Reflection.IsList(dataType);

Mapper/Linq/QueryVisitor.cs

@@ -107,7 +107,9 @@ private Query VisitExpression(Expression expr, string prefix = null)
 #else
                 var type = met.Method.DeclaringType;
 #endif
-                var paramType = (met.Arguments[0] as MemberExpression)?.Expression.NodeType;
+                var paramType = met.Arguments[0] is MemberExpression ? 
+                    (ExpressionType?)(met.Arguments[0] as MemberExpression).Expression.NodeType :
+                    null;
 
                 // StartsWith
                 if (method == "StartsWith")

Mapper/Reflection/Reflection.cs

@@ -72,10 +72,9 @@ public static GenericSetter CreateGenericSetter(Type type, MemberInfo memberInfo
                 else return null; // no field on Structs
             }
 #endif
-            var dataType =
-                (memberInfo as PropertyInfo)?.PropertyType ??
-                (memberInfo as FieldInfo)?.FieldType ??
-                typeof(object);
+            var dataType = memberInfo is PropertyInfo ?
+                (memberInfo as PropertyInfo).PropertyType :
+                (memberInfo as FieldInfo).FieldType;
 
             var target = Expression.Parameter(typeof(object), "obj");
             var value = Expression.Parameter(typeof(object), "val");