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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What is dh4o from Listing 7, however, is that its usage is arguably not much simpler than the basic QBE version shown already:. LINQ support is fully integrated in db4o for. Rollback only undoes uncommitted changes in the database. You need it to compile vb4o examples. When an object is stored into an object database, a unique key is created, called an Object identifier or OID pronounced similarly to the last syllable of avoidwhich uniquely identifies that object.
QBE is the preferred mechanism for simple query situations because it’s an easier API to work with, but it does require that your domain objects permit any or all of the fields containing data to be set to null, documentatioon may violate some of your domain rules. From Wikipedia, the free encyclopedia.
Getting Started With db4o
However, this mode has limitations. Best for servers and concurrent environments. Methods available on this class vary from release to release as they are introduced, removed, or moved to the core ObjectContainer class itself.
About this series Information storage and retrieval has been nearly synonymous with RDBMS for about a decade now, but recently that has begun to change. Here is the query syntax:. Matching values will NOT equal the supplied value. Whenever you start making changes to your database using the Store and Delete commands you are automatically in an open transaction.
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DefragmentConfig (db4o – database for objects – documentation)
For strings, matches will start with the supplied value. For strings, matches will end with the supplied value. This will copy the necessary db4o libraries to your application’s bin folder automatically when compiling your project. Using Port 0 for your server creates an “Embedded” server which will not be available remotely. Here’s one quick and easy example that gets all of the Customers with “Smith” in their name, and sorts the results by name.
Native Query results can be sorted by using an IComparer or a comparison delegate. It can run on any operating system that supports Java or. Fetching a million objects is not something even the hardiest hardware will shrug off easily, particularly if it’s across a network connection. Performs a negation comparison. The application developer should tune the number of indexes with the desired Query and Insert performance. The default ActivationDepth in db4o is 5. So QBE can be used only to retrieve exact-value matches.
For strings, matching values will contain the supplied value anywhere within the match. 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 I also leave it as an exercise to the reader to decide which is the case here. October Learn how and when to remove this template message.
Docuentation you wish to cancel or roll back any uncommitted changes, use the Rollback method:. An iterator is created against the best index found. Due to a feature referred to as “Generic Reflection”, db4o can work without implementing persistent classes on the server.
Documsntation can also be used as an abstraction layer, allowing to easily switch the underlying database technology. Optimization is still done inside the database, but instead of text being returned real objects are sent back, ready for use.
The busy Java developer’s guide to db4o: Queries, updates, and identity
WriteLine in C causes the optimizer to fail in the. Astute readers of Joshua Bloch’s Effective Java will notice that I’ve left out the hashCode implementation, a clear violation of Rule 8. It will not undo changes to any currently loaded objects. While a db4o dbb4o file is open, it is locked and cannot be accessed by another application at the same time. LINQ Queries have all the benefit of compiler checking and automated code refactorability that Native Queries have, but documentatioh expressed in syntax more familiar to SQL developers.
OME was initially suggested to customers as a commercial product only available to dDN subscribers. Let’s start with a basic premise: As explained in the section on Dealing docymentation Object Activation, the ActivationDepth controls how much data is loaded when an object is retrieved from the database.
Fine-grained activation depth can be configured per class. Communication is implemented through messaging.
In the classic parlance of authors everywhere, I leave hashCode as “an exercise to the reader,” which typically means the author either doesn’t want to bother with it or doesn’t think it’s necessary to the example documenattion hand.