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New primary key documentation.

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Jim Menard 2009-02-01 09:14:21 -05:00
parent 2748338deb
commit f94ad318b6
1 changed files with 29 additions and 8 deletions
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README.rdoc
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@ -121,13 +121,27 @@ Mongo as-is. If the string is ASCII all is well, because ASCII is a subset of
UTF-8. If the string is not ASCII then it may not be a well-formed UTF-8
string.
== The DB class
== Primary Keys
The field _id is a primary key. It is treated specially by the database, and
its use makes many operations more efficient.
The value of an _id may be of any type. (Older versions of Mongo required that
they be XGen::Mongo::Driver::ObjectID instances.)
The database itself inserts an _id value if none is specified when a record is
inserted.
=== Primary Key Factories
A basic Mongo driver is not responsible for creating primary keys or knowing
how to interpret them. You can tell the Ruby Mongo driver how to create
primary keys by passing in the :pk option to the Mongo#db method.
A primary key factory is a class you supply to a DB object that knows how to
generate _id values. Primary key factories are no longer necessary because
Mongo now inserts an _id value for every record that does not already have
one. However, if you want to control _id values or even their types, using a
PK factory lets you do so.
You can tell the Ruby Mongo driver how to create primary keys by passing in
the :pk option to the Mongo#db method.
include XGen::Mongo::Driver
db = Mongo.new.db('dbname', :pk => MyPKFactory.new)
@ -163,10 +177,17 @@ ActiveRecord-like framework for non-Rails apps) and the AR Mongo adapter code
end
end
A database's PK factory object may be set after you obtain it, but only once.
The only reason it is changeable is so that libraries such as MongoRecord that
use this driver can set the PK factory after obtaining the database but before
using it for the first time.
A database's PK factory object may be set either when a DB object is created
or immediately after you obtain it, but only once. The only reason it is
changeable at all is so that libraries such as MongoRecord that use this
driver can set the PK factory after obtaining the database but before using it
for the first time.
== The DB Class
=== Primary Key factories
See the section on "Primary Keys" above.
=== Strict mode