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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Object data is activated as the users accesses each object in the result set.
Eric Falsken Something, Acme. The port parameter specifies the network port number.
MaxValue will cause all related objects to be instantiated as deeply as possible, restoring the entire object graph to memory. But oftentimes, you will want to configure specific behaviors per-class-type, or per-field. SomeClass here does not require any interface implementations, annotations or attributes added.
Queries, updates, and identity
Over a million developers have joined DZone. All of an object’s properties and child objects will be stored. Walks you through db4o’s basic operations, its various query types, and techniques for optimal data access performance. The Object Database ODB arrived in the software industry with the advent of object oriented languages. As always, see the db4o documentation for the complete details of the ExtObjectContainer class.
Db4o – Wikipedia
Best when queries must be deterministic or execute as quickly as possible. What is apparent from Listing 7, however, is that its usage is arguably not much simpler than the basic QBE version shown already:. Acceptable values are any number above which are not already in use. It can also be used as an abstraction layer, allowing to easily switch the underlying database technology. October Learn how and when to remove this template message. Performs a negation comparison.
If a field in the prototype is “null,” then that value dochmentation against any value in the data store; otherwise, the values must match exactly. This article relies too much on references to primary sources. Your changes will be permanently saved. Please discuss further on the talk page. The ODB is primarily used as an application specific database in either extreme scale systems or embedded systems where typical DBA activities are automated.
In this and future articles, I’ll continue making the case for the object database. Setting the ActivationDepth too aggressively can cause poor db4o query performance and high memory usage. It consists dicumentation one type, whose definition appears in Listing You can use the same Store object command to update an object.
Properties of the 5th descendant object will have their values left as default or null.
In this second article in The busy Java developer’s guide to db4oI used the OODBMS notion of identity as a launching point for explaining how db4o stores and retrieves objects, as well as introducing its native query facility. 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. 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.
The key thing to remember is that you can build convenience methods on top of the db4o infrastructure to make it easier to use. This feature can be viewed as an advantage over relational model, where any change in the schema results in mostly manual code review and upgrade to match the schema changes.
In the previous example, the query is looking for all Person types where the firstName field is equal to “Brian,” and the lastName and age fields are effectively ignored. The db4o Java distribution includes several jar files, including a core db4o implementation for each of the JDK 1.
The application developer should tune the number of indexes with the desired Query and Insert performance. Once that’s all done, I call get on the db4o database and check to see if the ObjectSet returned contains any objects.
Ted Neward Published on March 27, The db4o development team occasionally documentaton that certain APIs are less frequently used, or represent “experiments” on the API that the team isn’t sure should be a part of the core ObjectContainer API.