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.
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Information storage and retrieval has been nearly synonymous with RDBMS for about a decade now, but recently that has begun to change.
This multi-faceted approach to querying databases may strike you as complex and confusing and entirely different from how an RDBMS works. Query by Example QBE is a database query language that allows you to create queries by designing a “template” against which to do tutorlal, rather than a language using predicate criteria as in SQL.
Start with a look at dn4o admittedly primitive database. LINQ Queries have all the benefit of compiler checking and automated code refactorability that Native Queries db4i, but are expressed in syntax more familiar to SQL developers. Setting the UpdateDepth to 0 will prevent any changes from being saved to the database.
QBE queries also cannot query for value ranges greater than, less than or stringbased expressions contains, starts with. It consists of three fields and some basic methods to support POJO-like activities, namely toString and equals.
Optimization can also be done at buildtime using Db4oTool. This series is a working introduction to db4o, an open source database that leverages sb4o object-oriented languages, systems, and mindset. In this first example we will introduce D4bo.
A graph is a network of objects which represent a segment of data.
What hutorial apparent from Listing 7, however, is that its usage is arguably not much simpler than the basic QBE version shown already:. When searching for Brian in the database, you therefore need only look for those attributes on the Person instances. Although this makes for a fairly easy way to issue queries, it also makes for somewhat limited options; for example, what if you needed to retrieve dn4o Person s whose last name started with Gor all Person s of an age greater than 21?
Documents Ressources professionnelles Informatique. It can be assembled again in the morning, but one eventually asks whether this is the most efficient way to park a car. PDF for easy Reference. Depending on the features your application requires, reference and distribute these assemblies when you distribute your application:.
thtorial I have a db4o database in which I have a type Person that I want to query based on a set of fields that have certain values in them. NET Framework to be installed. ObjectContainer represents “The Database”, and will be your primary interface to db4o.
NET Framework version 3. When dealing with objects that may have relations to other objects quite deep think of the path of data from Customer to Order to OrderItem to Product with relations to Address objects for billing and shipping and then PO and payment transactions it would be quite expensive to have to pull all of that data into memory from the DB if all you wanted was the Customer object. QBE lets you pass db4o an example object.
The second option pollutes the simplicity of the QBE approach and leads to monstrosities like the one shown in Listing Refcard Getting Started With db4o. The IConfiguration object must be passed in the call to open the db4o file, server, or client connection. This content is part of the series: 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.
The currently stored state is used when activating field data, not the object state at the time of query execution.
Getting Started With db4o
Walking the results is a simple exercise in using the Iterator interface implemented by ObjectSet. For strings, matching values will contain the supplied value anywhere within the match. Developers can find this out, but only in a passive fashion, using the listeners described in this section. NET Object Data Walks you through db4o’s basic operations, its various query types, and techniques for optimal data access performance.
For all but the simplest db4o use cases, you’ll probably want to specify one or more configuration settings when opening your db4o database: The db4o container doesn’t run into problems of identity here because the object in question has already been identified as one coming from the database, meaning its OID is already stored inside the db4o bookkeeping infrastructure.
We said earlier that when calling Store to update an object graph, that db4o will not by default descend into child objects to detect changes to the graph.
sb4o Here’s one quick and easy example that gets all of the Customers with “Smith” in their name, and sorts the results by name. Over a million developers have joined DZone. This also points out a limitation of the QBE approach — zero cannot effectively be used as a value to search on. Tutorila is useful for multi-threaded operations or web-server style environments where you wish to handle parallel operations in a single process. Versant Corporation supports the db4o team and open source community.
In the classic parlance of authors everywhere, I leave hashCode as “an exercise tutorail 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 at hand. The default value of 5 is a good balance for most applications, but developers should balance this against the weight of their classes and their access patterns.
The busy Java developer’s guide to db4o: Queries, updates, and identity
It is maintained online. Using combinations of SODA query and constraint keywords, you can build up what is called a query “graph”. An iterator is created against the best index found.