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Using database API

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{{man warn|If you are a looking for documentation on how to use the GRAMPS Gramps system as a user instead of as a program developer, it can be found on the [[Portal:Using_GRAMPSUsing_Gramps|GRAMPS Gramps documentation web page]].}}
Explanation of the basics, underlying GRAMPS Gramps database. '''This is not intended to be a reference manual''', but an introductory programmer's guide to using the GRAMPS Gramps database access routines.
Separate [httphttps://www.gramps-project.org/docs/ API Reference Documentation for current version 3.3.0 of GRAMPSGramps] and as well as a simple [[Media:API.svg|UML (svg) diagram for 34.41.x]] and [[Gramps Data Model]] overview are available.
GRAMPS Gramps is written in the [http://www.python.org Python] language. A basic familiarity with Python is required before the database objects can be effectively used. If you are new to Python, you may wish to check out the [httphttps://docs.python.org/tut2/tuttutorial/ Python 2.html x tutorial] or [https://docs.python.org/3/tutorial/ Python 3.x tutorial].
== Database API ==
The full database hierarchy is:
* '''DbBsddb''' - read and write implementation to BSDDB databases ([http://gramps.svn.sourceforge.net/viewvcp/gramps/trunksource/srcci/master/tree/gramps/gen/db/write.py?view=markup gen/db/write.py])** '''DbWriteBase''' - virtual and implementation-independent methods for reading data ([http://gramps.svn.sourceforge.net/viewvcp/gramps/trunksource/ci/srcmaster/tree/gramps/gen/db//base.py?view=markup gen/db/base.py])** '''DbBsddbRead''' - read-only (accessors, getters) implementation to BSDDB databases ([http://gramps.svn.sourceforge.net/viewvcp/gramps/trunksource/ci/master/srctree/gramps/gen/db/read.py?view=markup gen/db/read.py])*** '''DbReadBase''' - virtual and implementation-independent methods for reading data ([http://gramps.svn.sourceforge.net/viewvcp/gramps/trunksource/ci/master/tree/srcgramps/gen/db/base.py?view=markup gen/db/base.py])*** '''Callback''' - callback and signal functions ([http://gramps.svn.sourceforge.net/viewvcp/gramps/trunksource/srcci/master/tree/gramps/gen/utils/callback.py?view=markup gen/utils/callback.py])** '''UpdateCallback''' - callback functionality ([http://gramps.svn.sourceforge.net/viewvcp/gramps/trunksource/ci/master/tree/srcgramps/gen/db/readupdatecallback.py?view=markup gen/updatecallback.py])** '''DbTxn''' - class for managing Gramps transactions and the undo database ([http://gramps.svn.sourceforge.net/viewvcp/gramps/trunksource/ci/master/tree/srcgramps/gen/db/txn.py??view=markup gen/bddb/txn.py])* '''DbDjangoDbGeneric''' - general read and write implementation to Django-based databases ([http://gramps.svn.sourceforge.net/viewvc/gramps/trunk/src/web/dbdjango.py?view=markup web/dbdjango.py])implementations** '''DbWriteBase''' - virtual and implementation-independent methods for reading data ([http://gramps.svn.sourceforge.net/viewvcp/gramps/trunksource/srcci/master/tree/gramps/gen/db/base.py?view=markup gen/db/base.py])** '''DbReadBase''' - virtual and implementation-independent methods for reading data ([http://gramps.svn.sourceforge.net/viewvcp/gramps/trunksource/ci/master/tree/srcgramps/gen/db//base.py?view=markup gen/db/base.py])
=== DbBsddb ===
The DbBsddb interface defines a hierarchical database (non-relational) written in [http://www.jcea.es/programacion/pybsddb.htm PyBSDDB]. There is no such thing as a database schema, and the meaning of the data is defined in the Python classes above. The data is stored as pickled tuples and unserialized into the [[Using_database_API#Primary_Objects|primary data types (below)]].
=== DbDjango DB-API ===
The DbDjango DB-API interface defines the Gramps data in terms of ''models'' and ''relations'' from uses a generic interface backed with the general Python SQL implementation, called [httphttps://www.djangoprojectpython.comorg/dev/peps/ Django projectpep-0249/ DB-API]. The Gramps' generic interface (gramps.gen.db.generic.DbGeneric) has all of the logic for interacting with the database backend can be any implementation that supports Django, including such popular except for the specific DB access code. Gramps' DB-API (gramps.plugins.db.dbapi.dbapi) implements the details so as to talk to conforming SQL implementations as sqlite, MySQL, Postgresql, and Oracledatabases. The data is retrieved from Other database engines could also implement the SQL fieldsDbGeneric details, serialized and then unserialized into the primary data types (below)such as a nosql option.
For more details on the By default, Gramps DB-API uses sqlite. However, you can also configure DB-API to use mysql, postgresql, and perhaps others. To be compatible with BSDDB, DB-API stores Gramps Django projectdata in an identical manner (pickled tuples). However, to allow for fast access, DB-API also stores "flat" data (such as strings and integers) in secondary SQL fields. These are indexed so that data can be selected without having to traverse, unpickle, initialize objects, see [[GEPS 013: GRAMPS Webapp]]and compare properties.
=== Using the Database ===
==Primary Objects==
Primary objects are the fundamental objects in the GRAMPS Gramps database. These objects are:* [http://www.gramps-project.org/docs/gen/gen_lib.html#module-gramps.gen.lib.person Person] - Contains the information specific to an individual person.* [http://www.gramps-project.org/docs/gen/gen_lib.html#module-gramps.gen.lib.family Family] - Contains the information specific to relationships between people. This typically contains one or two parents and zero or more children.* [http://www.gramps-project.org/docs/gen/gen_lib.html#module-gramps.gen.lib.event Event] - Contains the information related to an event. The event is treated as a primary object in the database, it currently does not appear as a primary object to the end user.* [http://www.gramps-project.org/docs/gen/gen_lib.html#module-gramps.gen.lib.place Place] - Contains the information related to a specific place.* [http://www.gramps-project.org/docs/gen/gen_lib.html#module-gramps.gen.lib.src Sourcerepo Repository] - Contains the information related to a source of informationrepository.* Citation [http://www.gramps-project.org/docs/gen/gen_lib.html#module-gramps.gen.lib.src Source] - Contains the information related to a citation into a sourceof information.* [http://www.gramps-project.org/docs/gen/gen_lib.html#module-gramps.gen.lib.mediaobj Media Objectcitation Citation] - Contains the information related to a media object. This includes images, documents, or any other type of related filescitation into a source.* [http://www.gramps-project.org/docs/gen/gen_lib.html#module-gramps.gen.lib.repo Repositorymediaobj Media Object] - Contains the information related to a repositorymedia object. This includes images, documents, or any other type of related files.* [http://www.gramps-project.org/docs/gen/gen_lib.html#module-gramps.gen.lib.note Note] - Contains the information related to a note.
# urls
# lds_ord_list
# source_listcitation_list
# note_list
# change
# attribute_list
# lds_seal_list
# source_listcitation_list
# note_list
# change
# handle
# gramps_id
# the_typetype
# date
# description
# place
# source_listcitation_list
# note_list
# media_list
# attribute_list
# change
# tag_list
# private
# gramps_id
# title
# long(longitude)# lat(latitude)# main_locplaceref_list# alt_locname# alt_names# place_type# code# urlsalt_loc (deprecated)
# media_list
# source_listcitation_list
# note_list
# change
# tag_list
# private
# title
# author
# pubinfo(publication information)
# note_list
# media_list
# abbrev(abbreviation)
# change
# datamapattribute_list
# reporef_list
# tag_list
# private
# handle
# gramps_id
..# date# page# confidence# source_handle# note_list# media_list# attribute_list# change# tag_list# private
===7. Media:===
# path
# mime
# desc(description)# checksum
# attribute_list
# source_listcitation_list
# note_list
# change
# gramps_id
# type
# name
# note_list
# address_list
# urls
# change
# tag_list
# private
== Secondary Objects ==
In addition, there are a number of secondary objects. In the DbBsddb implementation, these are stored in the primary objects. Typically, this means that DbBsddb objects are stored in [httphttps://wwwdocs.python.org/doc/current3.4/liblibrary/module-pickle.html pickled] format. In the DbDjango implemetation, the secondary objects are additional tables.
The secondary objects include dates, addresses, and source references among other objects.
For this reason, it is always necessary to have reference to the database that contains the objects with which you are working.
The handle should not be visible to the end user, and should not be included in reports or displayed on screen. Instead, the GRAMPS Gramps ID value should be used for this purpose. The GRAMPS Gramps ID is a user defined value for each object, but is not used internally to the database. This allows the user to change the GRAMPS Gramps ID without affecting the database.
Once created, the handle should never be modified.
person1.set_nickname('Fred')
</pre>
In this case, even though person1 and person2 represent the same person, but they are distinct objects. Changing the nickname of person1 does not affect person2. The person2 object will retain the original nickname.
Changes to the object do not become permanent until the object has been committed to the database. If multiple instances exist in memory at the same time, care must be taken to make sure that data is not lost.
==Database Objects==
GRAMPS Gramps provides a standard interface for all database objects. The GRAMPS Gramps database object provides the interface to the lower level database. Currently, only one database interface is supported:
* GrampsBSDDB - the default database, providing access to a Berkeley DB database.
===Transactions and Commits===
In order to support an UNDO feature, the database has the concept of [httphttps://gramps-project.org/docs/gen/gen_db.html#bsddbmodule-gramps.gen.db.txn Transactions].
Transactions are a group of related database commit operations that need treated as a single unit. If all related commits are not undone as a single unit, the database can be left in a corrupted state. The UNDO operation will undo all the commits in the transaction.
===Iterating through the database===
Frequently, it is useful to iterate through all the elements of a database. GRAMPS Gramps provides two ways of accomplishing this. The first method involves getting a list of all the handles and looping over the list. This method is the easiest to implement. An example is below:
for handle in database.get_person_handles():
person = database.get_person_from_handle(handle)
A more efficient method exists, but is more complicated to use. The database can provide a [httphttps://www.gramps-project.org/devdocdocs/apigen/2gen_db.2/private/GrampsDbhtml#module-gramps._GrampsDbBasegen.GrampsCursor-classdb.html cursor cursor] that will iterate through the database without having to load all handles into memory. The cursor returns a handle, data pair. The data represents the serialized data directly from the database. It is the users responsibility to unserialize the data. An example is below:
cursor = database.get_person_cursor()
pair = cursor.first()
===Getting notification of changes to the database===
If you have widgets that are displaying the content of the database tables you need to be aware that the database can change. Records may be added, removed or updated by other parts of GRAMPS Gramps and your widget must show these changes. The GRAMPS Gramps database provides a signalling mechanism that can be used to notify your widget of changes to the database. The documentation for the ((GrampsDBCallback)) class provides a description of the signalling mechanism. For most code that uses the GRAMPS Gramps database all that is required is for callback functions to be connected to the correct signals. For example:
database.connect('person-add',self.update_view)
database.connect('person-update',self.update_view)
database.connect('person-rebuild',self.update_view)
A full list of the signals that are emitted from the database can be found at the top of the <tt>[https://gramps-project.org/docs/gen/gen_db.html#module-gramps.gen.db.base GrampsDbBase]</tt> class in the <tt>GrampsDbBase[https://github.com/gramps-project/gramps/blob/master/gramps/gen/db/base.py gramps/gen/db/base.py]</tt> module.
[[Category:Developers/Tutorials]]

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