Difference between revisions of "Databases"

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|[[Database Module#db:open|db:open]]
 
|[[Database Module#db:open|db:open]]
|db:open("db", "path/to/docs")
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|{{Code|db:open("db", "path/to/docs")}}
 
|Returns all documents that are found in the database {{Code|db}} at the (optional) path {{Code|path/to/docs}}.
 
|Returns all documents that are found in the database {{Code|db}} at the (optional) path {{Code|path/to/docs}}.
 
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|[http://www.xqueryfunctions.com/xq/fn_collection.html fn:collection]
 
|[http://www.xqueryfunctions.com/xq/fn_collection.html fn:collection]
|collection("db/path/to/docs")
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|{{Code|collection("db/path/to/docs")}}
 
|Returns all documents at the location {{Code|path/to/docs}} in the database {{Code|db}}.<br/>If no path is specified after the database, all documents in the database will be returned.<br/>If no argument is specified, all documents of the database will be returned that has been opened in the global context.
 
|Returns all documents at the location {{Code|path/to/docs}} in the database {{Code|db}}.<br/>If no path is specified after the database, all documents in the database will be returned.<br/>If no argument is specified, all documents of the database will be returned that has been opened in the global context.
 
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|[http://www.xqueryfunctions.com/xq/fn_doc.html fn:doc]
 
|[http://www.xqueryfunctions.com/xq/fn_doc.html fn:doc]
|doc("db/path/to/doc.xml")
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|{{Code|doc("db/path/to/doc.xml")}}
 
|Returns the document at the location {{Code|path/to/docs}} in the database {{Code|db}}.<br/>An error is raised if the specified yields zero or more than one document.
 
|Returns the document at the location {{Code|path/to/docs}} in the database {{Code|db}}.<br/>An error is raised if the specified yields zero or more than one document.
 
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!Description
 
!Description
 
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|{{Code|db:name($node)}}
 
|{{Code|db:name($node)}}
 
|Returns the name of the database in which the specified {{Code|$node}} is stored.
 
|Returns the name of the database in which the specified {{Code|$node}} is stored.
 
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|<code>[[Database Module#db:path|db:path]]</code>
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|[[Database Module#db:path|db:path]]
 
|{{Code|db:path($node)}}
 
|{{Code|db:path($node)}}
 
|Returns the path of the database document in which the specified {{Code|$node}} is stored.
 
|Returns the path of the database document in which the specified {{Code|$node}} is stored.

Revision as of 12:37, 23 January 2016

This page is part of the Getting Started Section.

In BaseX, a database is a pretty light-weight concept and can be compared to a collection. It contains an arbitrary number of resources, addressed by their unique database path. Resources can either be XML documents or raw files (binaries). Some information on binary data can be found on an extra page.

Create Databases

New databases can be created via commands, in the GUI, or with any of our APIs. If some input is specified along with the create operation, it will be added to the database in a bulk operation:

  • Console: CREATE DB db /path/to/resources will add initial documents to a database
  • GUI: Go to DatabaseNew, press Browse to choose an initial file or directory, and press OK

Database must follow the valid names constraints. Various parsers can be chosen to influence the database creation, or to convert different formats to XML.

Note: A main-memory only database can be created using the the SET MAINMEM true command before calling CREATE DB (see below for more).

Access Resources

Stored resources and external documents can be accessed in different ways:

XML Documents

Various XQuery functions exist to access XML documents in databases:

Function Example Description
db:open db:open("db", "path/to/docs") Returns all documents that are found in the database db at the (optional) path path/to/docs.
fn:collection collection("db/path/to/docs") Returns all documents at the location path/to/docs in the database db.
If no path is specified after the database, all documents in the database will be returned.
If no argument is specified, all documents of the database will be returned that has been opened in the global context.
fn:doc doc("db/path/to/doc.xml") Returns the document at the location path/to/docs in the database db.
An error is raised if the specified yields zero or more than one document.

You can access multiple databases in a single query:

for $i in 1 to 100
return db:open('books' || $i)//book/title

If the DEFAULTDB option is turned on, the path argument of the fn:doc or fn:collection function will first be resolved against the globally opened database.

Two more functions are available for retrieving information on database nodes:

Function Example Description
db:name db:name($node) Returns the name of the database in which the specified $node is stored.
db:path db:path($node) Returns the path of the database document in which the specified $node is stored.

The fn:document-uri and fn:base-uri functions return URIs that can also be reused as arguments for the fn:doc and fn:collection functions. As a result, the following example query always returns true:

every $c in collection('anyDB')
satisfies doc-available(document-uri($c))

If the argument of fn:doc or fn:collection does not start with a valid database name, or if the addressed database does not exist, the string is interpreted as URI reference, and the documents found at this location will be returned. Examples:

  • doc("http://web.de"): retrieves the addressed URI and returns it as a main-memory document node.
  • doc("myfile.xml"): retrieves the given file from the file system and returns it as a main-memory document node. Note that updates to main-memory nodes are not automatically written back to disk unless the WRITEBACK option is set.
  • collection("/path/to/docs"): returns a main-memory collection with all XML documents found at the addressed file path.

Raw Files

Updated with Version 8.4: items of binary type can be output without specifying the obsolete raw serialization method.

The RETRIEVE command and the db:retrieve function can be used to return files in their native byte representation.

If the API you use does not support binary output (this is e.g. the case for various Client language bindings), you need to convert your binary data to its string representation before returning it to the client:

string(db:retrieve('multimedia', 'sample.avi'))

HTTP Services

  • With REST and WebDAV, all database resources can be requested in a uniform way, no matter if they are well-formed XML documents or binary files.

Update Resources

Once you have created a database, additional commands exist to modify its contents:

  • XML documents can be added with the ADD command.
  • Raw files are added with STORE.
  • Existing resources can be replaced with the REPLACE command.
  • Resources can be deleted via DELETE.

The AUTOFLUSH option can be turned off before bulk operations (i.e. before a large number of new resources is added to the database).

The ADDCACHE option will first cache the input before adding it to the database. This is helpful when the input documents to be added are expected to eat up too much main memory.

The following commands create an empty database, add two resources, explicitly flush data structures to disk, and finally delete all inserted data:

CREATE DB example
SET AUTOFLUSH false
ADD example.xml
SET ADDCACHE true
ADD /path/to/xml/documents
STORE TO images/ 123.jpg
FLUSH
DELETE /

You may as well use the BaseX-specific XQuery Database Functions to create, add, replace, and delete XML documents:

let $root := "/path/to/xml/documents/"
for $file in file:list($root)
return db:add("database", $root || $file)

Last but not least, XML documents can also be added via the GUI and the Database menu.

Export Data

All resources stored in a database can be exported, i.e., written back to disk. This can be done in several ways:

  • Commands: EXPORT writes all resources to the specified target directory
  • GUI: Go to DatabaseExport, choose the target directory and press OK
  • WebDAV: Locate the database directory (or a sub-directory of it) and copy all contents to another location

In Memory Database

  • In the standalone context, a main-memory database can be created (using CREATE DB), which can then be accessed by subsequent commands.
  • If a BaseX server instance is started, and if a database is created in its context (using CREATE DB), other BaseX client instances can access (and update) this database (using OPEN, db:open, etc.) as long as no other database is opened/created by the server.

Note: main-memory database instances are also created by the invocation of doc(...) or collection(...), if the argument is not a database (no matter which value is set for MAINMEM). In other words: the same internal representation is used for main-memory databases and documents/collections generated via XQuery.

Changelog

Version 8.4
  • Updated: Raw Files: Items of binary type can be output without specifying the obsolete raw serialization method.
Version 7.2.1
  • Updated: fn:document-uri and fn:base-uri now return strings that can be reused with fn:doc or fn:collection to reopen the original document.