Data Structure
LiteDB stores data as documents, which are JSON-like objects containing key-value pairs. Documents are a schema-less data structure. Each document stores both its data and its structure.

{
    _id: 1,
    name: { first: "John", last: "Doe" },
    age: 37,
    salary: 3456.0,
    createdDate: { $date: "2014-10-30T00:00:00.00Z" },
    phones: ["8000-0000", "9000-0000"]
}
_id contains document primary key - a unique value in collection
name contains an embedded document with first and last fields
age contains a Int32 value
salary contains a Double value
createDate contains a DateTime value
phones contains an array of String
LiteDB stores documents in collections. A collection is a group of related documents that have a set of shared indices. Collections are analogous to tables in relational databases.

BSON
LiteDB stores documents using BSON (Binary JSON). BSON is a binary representation of JSON with additional type information. In the documents, the value of a field can be any of the BSON data types, including other documents, arrays, and arrays of documents. BSON is a fast and simple way to serialize documents in binary format.

LiteDB uses only a subset of BSON data types. See all supported LiteDB BSON data types and .NET equivalents.

BSON Type	.NET type
MinValue	-
Null	Any .NET object with null value
Int32	System.Int32
Int64	System.Int64
Double	System.Double
Decimal	System.Decimal
String	System.String
Document	System.Collection.Generic.Dictionary<string, BsonValue>
Array	System.Collection.Generic.List<BsonValue>
Binary	System.Byte[]
ObjectId	LiteDB.ObjectId
Guid	System.Guid
Boolean	System.Boolean
DateTime	System.DateTime
MaxValue	-
 Following the BSON specification, DateTime values are stored only up to the miliseconds. All DateTime values are converted to UTC on storage and converted back to local time on retrieval.
Extended JSON
To serialize a BSON document to JSON, LiteDB uses an extended version of JSON so as not to lose any BSON type information. Extended data types are represented as embedded documents, using a key starting with $ and string value.

BSON data type	JSON representation	Description
ObjectId	{ "$oid": "507f1f55bcf96cd799438110" }	12 bytes in hex format
Date	{ "$date": "2015-01-01T00:00:00Z" }	UTC and ISO-8601 format
Guid	{ "$guid": "ebe8f677-9f27-4303-8699-5081651beb11" }	
Binary	{ "$binary": "VHlwZSgaFc3sdcGFzUpcmUuLi4=" }	Byte array in base64 string format
Int64	{ "$numberLong": "12200000" }	
Decimal	{ "$numberDecimal": "122.9991" }	
MinValue	{ "$minValue": "1" }	
MaxValue	{ "$maxValue": "1" }	
LiteDB implements JSON in its JsonSerializer static class.

If you want to convert your object type to a BsonValue, you must use a BsonMapper.

var customer = new Customer { Id = 1, Name = "John Doe" };

var doc = BsonMapper.Global.ToDocument(customer);

var jsonString = JsonSerialize.Serialize(doc);
JsonSerialize also supports TextReader and TextWriter to read/write directly from a file or Stream.

ObjectId
ObjectId is a 12 bytes BSON type:

Timestamp: Value representing the seconds since the Unix epoch (4 bytes)
Machine: Machine identifier (3 bytes)
Pid: Process id (2 bytes)
Increment: A counter, starting with a random value (3 bytes)
In LiteDB, documents are stored in a collection that requires a unique _id field that acts as a primary key. Because ObjectIds are small, most likely unique, and fast to generate, LiteDB uses ObjectIds as the default value for the _id field if the _id field is not specified.

Unlike the Guid data type, ObjectIds are sequential, so it’s a better solution for indexing. ObjectIds use hexadecimal numbers represented as strings.

var id = ObjectId.NewObjectId();

// You can get creation datetime from an ObjectId
var date = id.CreationTime;

// ObjectId is represented in hex value
Debug.WriteLine(id);
"507h096e210a18719ea877a2"

// Create an instance based on hex representation
var nid = new ObjectId("507h096e210a18719ea877a2");