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Delphi MongoDB driver
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Delphi MongoDB Driver

A Delphi driver to access a mongoDB server.
It maps variables onto Delphi variables of type OleVariant, which resembles
the loose typing of JavaScript.
There are two main units and three main classes to enable access to a mongo DB 

  TBSONDocument = class(TInterfacedObject, IBSONDocument, IPersistStream)
    Holds the data of a 'document', the basic unit of data mongoDB works with.
    Implements an IBSONDocument interface which allows it to be referenced by
	an OleVariant variable, which enables embedding documents.
    Implements the IPersistStream interface to enable loading from and saving
	to BSON, the internal binary storage specification used by mongoDB.

  function BSON: IBSONDocument; overload;
  function BSON(x: array of OleVariant): IBSONDocument; overload;
    Creates a BSON document object ready for use.
    Optionally pass a sequence of key-value pairs,
	  e.g.: BSON(['x',5,'y',7]);
    Use '[' and ']' to created embedded documents,
	  e.g.: BSON(['x','[','$gt',7,']']);
    Use VarArrayOf or 1-dimensional variant arrays to add arrays,
	  e.g.: BSON(['x',VarArrayOf([1,2,3])]);
  function BSONenum: IBSONDocumentEnumerator;
    See below

    A connection to a mongoDB server. Supports getting single items, 
	performing inserts, updates and deletes.

    A query to a mongoDB server, handles the cursor and subsequent requests to
	the server to get more data when needed.

Additional tools

  function BsonToJson(Doc: IBSONDocument): WideString;
    Converts a BSON document into a JSON string.
  function JsonToBson(jsonData: WideString): IBSONDocument;
    Converts a JSON string into a BSON document.
  procedure JsonIntoBson(jsonData: WideString; doc: IBSONDocument); overload;
    Parses a JSON string and adds any keys to an existing BSON document,
	overwriting the value if a key already exists.
  procedure JsonIntoBson(jsonData: WideString; doc: IBSONDocument;
    var EndIndex:integer); overload;
    Parses only the first JSON object from a string into an existing BSON
	document, and returns the index into the string where the JSON object
	ends. Use this method to iterate over a list of JSON strings.
	(See also IBSONDocument.Clear)

BSON document enumerator

In scenario's where you have BSON documents that contain one or more arrays of
other BSON documents, parsing the data into the total number of BSON document
instances required, may take a lot of memory and have an impact on performance.
This is in disaccord with the fact that most probably the children documents
get processed one by one.

To improve this scenario, you can use IBSONDocumentEnumerator. The Load method
of the default IBSONDocument implementation detects if an
IBSONDocumentEnumerator instance is present when it is about to parse an
embedded document in an array. If there is, the IBSONDocumentEnumerator
instance is loaded with an extra reference to the storage stream and the
stream positions of the documents in the array, but the internal
structure is not parsed yet. (Attention: since the enumerator keeps a
reference to the storage stream, its lifetime may get extended past the
original IPersistStream.Load call.)

By using the enumerator's Next method on a single IBSONDocument instance, only
one document at a time is parsed. Since the default IBSONDocument
implementation keeps the current set of keys and children documents, no time
is wasted releasing and re-allocating memory for (almost) the same structure
of data.

Attention: IBSONDocumentEnumerator doesn't support updates (yet?). It's
available read-only, but doesn't enforce this. Modifications to the document
used with Next don't get updated.
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