why we can't Serialize objects into Random Access file ? and on the other hand we can serialize objects into sequential access file ?
""C# does not provide a means to obtain an object’s size at runtime. This means that, if we serialize the class, we cannot guarantee a fixed-length record size "" (from the book that i read in).
so we cannot read the the random access file because we don't know every object size in the file so how we could do seeking ??????
Any object marked with the SerializableAttribute attribute can be serialized (in most scenarios). The result from serialization is always directed to a stream, which may very well be a file output stream.
Are you asking why an object graph cannot be deserialized partially? .NET serialization only [de]serializes complete object graphs. Otherwise you'll have to turn to other serialization formatters, or write your own.
For direct random access to a file, you must open the file with a stream that supports seeking.
EDIT:
Seeking in the resulting stream from a serialization has no practical purpose - only the serialiation formatter knows what's in there anyway and should always be fed the very start of the stream.
For persisting the data into other structures; do it in a two-stage process: First, target the serialization bytes to a [i.e. memory-backed] stream that you can read the size from afterwards, then write the data to the actual backing store, using said knowledge of size.
You can't predict the size of a serialized object, because the serialized representation might differ a lot from the runtime representation.
It it still possible to achieve exact control over output size, if you use only primitive types, and you write using a BinaryWriter - but that is not serialization per-se.
The default binary serialization in .NET serializes a whole object graph, which, by its nature of being a graph, doesn't have a constant size, which means each serialization object (record) won't have a constant size, preventing random access.
To be able to randomly access any record in a file, write your own implementation of the binary serialization of your class, or use a database. If you need a simple, no-install single-threaded database engine, have a look at SQL Server Compact.
