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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This is useful for multi-threaded operations or web-server style environments where you wish to handle parallel operations in a single process. The busy Java developer’s guide to db4o http: LINQ was introduced by Microsoft. Development version provides the newest features and is released for testing, community feedback and evaluation.
DefragmentConfig (db4o – database for objects – documentation)
Special cases can be handled through writing custom type handlers. For example, including a console print statement System. Views Read Edit View history.
Learn how and when to remove these template messages. Please improve this by adding secondary or tertiary sources. Depending on the features your application requires, rocumentation and distribute these assemblies when you distribute your application:. Refcard Getting Started With db4o. 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.
If the bytecode is easy enough to understand, db4o will turn that query into a SODA query for efficiency, in which case there is no need to instantiate documenntation the objects to pass into the match method.
Free and open-source software portal. Query by Example QBE is a documentatuon 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.
While a simple display of data is interesting in itself, most objects will also need to be modified and restored back to the database. A list of object ID matches is generated completely when the query is executed and held in memory Lazy Best for limited resource environments. Setting the UpdateDepth too aggressively can cause poor db4o update performance. Note that the Descend method returns an IQuery too. Subscribe me to comment notifications. 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.
NQ can do all this because they are documentatiob as native. So QBE can be used only to retrieve exact-value matches. The default ActivationDepth in db4o is 5.
Setting the ActivationDepth too aggressively can cause poor db4o query performance and high memory usage. Over a million developers have joined DZone. Native Query results can be sorted by using an IComparer or a comparison delegate. MaxValue will cause all related objects to be instantiated as deeply as possible, restoring the entire object graph to memory.
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 You can keep references to those constraints and then use constraint keywords like AndOrand Not to relate the constraints together, as we did at the end of that example. This article may require cleanup to meet Wikipedia’s quality standards.
In db4o, the OID for a given object can be found through a call to db. I demonstrated data documntation using db4o’s QBE engine last time, but I’ll quickly recap here. A properly tuned activation depth is the best way to optimize retrieval of data from a db4o database.
By default, the db4o server runs in-process within your application. See ActivationDepth in the Configuration section for more ideas.
Practically speaking, this means you have to be more careful about objects-in-memory-versus-objects-in-storage when working with an object database. Developers can find this out, but only in a passive fashion, using the listeners described in this section.
But please don’t repeat that name dg4o the db4o developers; you’ll get me in trouble. This is probably the trickiest part of working with an OODBMS because an object database uses a different notion of identity from a relational database. All of an object’s properties and child objects will db4oo stored. Retrieved March 17, Once that’s all done, I call get on the db4o database and check to see if the ObjectSet returned contains any objects. Since the index snapshot is held in memory, the memory required varies greatly depending on what is being queried.
Fetching a million objects is not something even the hardiest hardware will shrug off easily, particularly if it’s across a network connection. Java developers in particular are frustrated with the so-called object-relational impedance mismatch, and impatient with the solutions that attempt to resolve it.
Queries, updates, and identity
The term object-oriented database system dates back to aroundthough the first research developments in this area started during the mids. Stable version is meant to be used in final product shipment. Documenattion you through db4o’s basic operations, its various query types, and techniques for optimal data access performance.