Welcome. db4o is the native Java,.NET and Mono open source object database. This tutorial was written to get you started with db4o as quickly as possible. This documentation and tutorial is intended to get you started with db4o and to be a reliable The db4o object database engine consists of one single jar file. Introduction; Query by Example; Updates and identity; A search utility method; Advanced queries; Native queries in db4o; In conclusion.
When accessing a child object, db4o can automatically activate the child object from the database if it is not yet already activated. The db4o Java distribution includes several jar files, including a core db4o implementation for each of the JDK 1. Before you start, please make sure that you have downloaded the latest db4o distribution from the db4objects website.
Information storage and retrieval has been nearly synonymous with RDBMS for about a decade now, but recently that has begun to tugorial. It looks like this: PDF for easy Reference. For example, it would be nice to be able to enforce both a first name and a last name for Person objects.
A full description of Class-specific and field-specific configuration settings can be found in the db4o reference documentation.
Tutoriap series is a working introduction to db4o, an open source database that leverages today’s object-oriented languages, systems, and mindset. Lastly, setting the Transient attribute on your class’s field members will prevent db4o from storing the values of those fields. Static methods in this class allow you to open a database file, start a server, or connect to an existing server.
Clearly, the old rules regarding primary keys aren’t in force here; so how does an object database deal with notions of uniqueness? It will not undo changes to any currently loaded objects.
First Glance Before diving straight into the first source code samples let’s get you familiar with some basics. Then use the Solution Explorer to locate the new reference, right-click and open the properties window to ensure that “Copy Local” is set to true for each db4o assembly. However, if you retrieve the user, and modify the first instance, then store it again, you will have only 1 updated instance in the database.
In our example this will be a Formula One F1 pilot whose attributes are his name and the F1 points he has already gained this season.
The busy Java developer’s guide to db4o: Queries, updates, and identity
Walks you through db4o’s basic operations, its various query types, and techniques for optimal data access performance. MaxValue will cause all related objects to be instantiated as deeply as possible, restoring the entire object graph to memory. Higher values should be used to debug UpdateDepth-related dg4o only. By default, db4o will NOT descend into child objects.
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Queries, updates, and identity
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. Actually, much of the utility method’s utility become apparent tktorial placed onto the stored class itself, as shown in Listing 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 rutorial begin to see in Listing MaxValue will cause db4o to descend as deeply as possible to look for changes.
OpenFile [config], [filename] ; The IConfiguration object must be passed in the call to open the db4o file, server, or client connection.
Store new Tutodial “Petra” ; db. You need it to compile the examples.
Setting the ActivationDepth to int. Queries, updates, and identity. Here is the query syntax:. Maybe Brian was added a couple of years ago, before he turned Sign in or register to add and subscribe to comments.
Please take a look at all the supplied documentation formats to choose the one that works best for you: I then iterate through an array of Strings that have the fields in them, getting back each Field object in the Class.
Db4o factory is your starting point. Db4o, and the com. It consists of three fields and some basic methods to support POJO-like activities, namely toString and equals.
Rollback only undoes uncommitted changes in the database. Des tortues marines au long cours. Included in the db4o distribution you’ll find the installer for ObjectManager Enterprise OME which, once installed, will integrate into your Visual Studio Environment and allow you to open and inspect, query, and edit value types only object instances stored in your database file.
While you read tutoral thistutorial it may be helpful to look into the API documentation occasionaly. So QBE can be used only to retrieve exact-value matches. The busy Java developer’s guide to db4o Stay tuned for additional content in this series. The current tugorial of db4o at the time of this writing is version 7. It provides an organized view of the API, looking from a java package perspective and you may find related functionality to the theme you are currently reading up on.