Visit the new documentation for updated content. DB4O. Table of contents. 1 Info; 2 The Basic Principle of db4o; 3 Downloads; 4 Current Status. This tutorial was written to get you started with db4o as quickly as possible. Before you The API documentation for db4o is supplied as a compiled Help file . db4o provides sources of documentation: tutorial, reference documentation, API documenation, online paircasts and.
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Getting Started With db4o
See ActivationDepth in the Configuration section for more ideas. Using tables to store objects is like driving your car home and then disassembling it to put it into the garage. In Listing 2, I create a half dozen of objects, place them into a file, and then use QBE to call up the two objects whose first names match the pattern “Brian. Almost no memory is needed to hold the result set.
Best when queries must be deterministic or execute as quickly as possible. If you wish to cancel or roll back any uncommitted changes, use the Rollback method:.
One of its main goals is to provide an easy and native interface to persistence for object oriented programming languages. Properties of the 5th descendant object will have their values left as default or null. Especially in a strongly typed language like C or Java programming, these object types have to be known a prioriunlike the set-based notion of SQL. Predictably, this would kill query performance, but you can work around it documentatio installing listeners where you need them.
It was developed, commercially licensed and supported by Actian. There is one more thing to be aware of: Refcard Getting Started With db4o. You can’t really anticipate variations of this type although you can learn about them by experienceso it’s always a good idea to Let The System Tell You, as they say in extreme programming. The community of db4o registered members grew to over 60, members. An iterator is created dlcumentation the best index found.
A full description of Class-specific and field-specific configuration settings can be found in the db4o reference documentation. What you need is a utility method to simplify identity-based searches.
The busy Java developer’s guide to db4o: Queries, updates, and identity
This is useful for multi-threaded operations or web-server style environments where you wish to handle parallel operations in a single process. LINQ was introduced by Microsoft.
As I explained, an object database like db4o simply has more to offer to object-oriented developers, in today’s object-oriented world, than its relational cousins. From the db4o version 7. The port parameter specifies the network port number. Accessing the results will simply iterate through the index until no further matches are found. You need it to compile the examples. It consists of one type, whose definition appears in Listing MaxValue will cause db4o to descend as deeply as possible to look for changes.
NET server and vice versa. Rather than force a complex query API onto developers or introduce a new “something-QL,” db4o offers a facility called native querieswhich is both powerful and remarkably easy to use, as you can begin to see in Listing In this worst-case scenario, db4o would have to instantiate every object of the queried type in the database and pass each one through the match implementation.
Query by Example QBE is a database query language that allows you to create queries by designing a “template” against which to do comparisons, rather than a language using predicate criteria as in SQL. If the database is not closed cleanly, or if the application crashes at any time and uncommitted or incomplete transactions are discarded.
A list of object ID matches is generated completely when the query is executed and held in memory. The busy Java developer’s guide to db4o Stay tuned for additional content in this series.
As explained in the section on Dealing with Object Activation, the Documnetation controls how much data is loaded when an object is retrieved from the database. This article may require cleanup to meet Wikipedia’s quality standards. The first commercial object database management systems were created in the early s; these added the concept of native database driven persistence into the field of object-oriented development.
Documentatlon you’ll see in a second, however, SODA is generally only necessary for hand-optimizing queries. And for those situations where db4o’s native query facility fails to meet the need, the SODA API which originally appeared as a standalone query system for any object system, and still lives on SourceForge allows you to tune the query down to its tiniest detail, at the expense of simplicity.
Walking the results is a simple exercise in using the Iterator interface implemented by ObjectSet. Using combinations of SODA query and constraint keywords, you can build up what is called a query “graph”.
For example, it would be nice to be able to enforce both a first cocumentation and a last name for Person objects. In db4o was purchased by Versant corporationwhich marketed it as open-source bi-licensed software: If the bytecode is easy enough to understand, db4o will documrntation that query into a SODA query for efficiency, in which case there is no need to instantiate all the objects to pass into docukentation match method.
By default, db4o will NOT descend into child objects. SomeClass here does not require any interface implementations, annotations or attributes added.
DefragmentConfig (db4o – database for objects – documentation)
LINQ Queries have all the benefit of compiler checking and automated code refactorability that Native Queries have, but are expressed in syntax more familiar to SQL developers. In this and future articles, I’ll continue dockmentation the case for the object database. It can run on any operating system that supports Java or. NET to access the database and thus avoid a constant, productivity-reducing context switch between programming language and data access API. This section shows you a solution based on using the Reflection APIs to poke the right values into the right fields, as well as suggesting ways to tune the solution for various preferences and aesthetics.
In OctoberActian declined to continue to actively pursue and promote the commercial db4o product offering for new customers.