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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Walking the results is a simple exercise in using the Iterator interface implemented by ObjectSet. Please help improve this article if you can.
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. You need it to compile the examples.
There is one more thing to be documentarion of: Using Port 0 for your server creates an “Embedded” server which will not be available remotely. Free and open-source software portal.
Getting Started With db4o
Despite its name, this is a Java bytecode optimizer developed at Purdue University that must be present, along with the db4o NET Framework version 3. LINQ was introduced by Microsoft.
Accordingly, when you call setdb4o knows to update the existing object rather than insert a new one. When searching for Brian in the database, you therefore need only look for those attributes on the Person instances.
While a simple display of data is interesting in itself, most objects will also need to be modified and restored back to the database. Object data is activated as the users accesses each object in the result set.
The db4o Java distribution includes several jar files, including a core db4o implementation for each of the JDK 1. About this series Information storage and retrieval db4p been nearly synonymous with RDBMS for about a decade now, but recently that has begun to change.
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 all Person s whose last name started with Gor all Person s of an age greater than 21?
Acceptable values are any number above which are not already in use. It consists of three fields and some basic documetation to support POJO-like activities, namely toString and equals. The result set can be influenced by subsequent transactions in the current context or by other clients causing possible concurrency errors. I demonstrated data retrieval using db4o’s QBE engine last time, but I’ll quickly recap here.
Sign in or register to add and documentaiton to comments. It may require cleanup to comply with Wikipedia’s content policies, particularly neutral point of view. In truth, this isn’t quite the case: This article has multiple issues. In Listing 2, I create a half dozen of objects, place them into a file, and then use QBE to call up the two objects whose first names match the pattern “Brian.
The busy Java developer’s guide to db4o: Queries, updates, and identity
No cleanup reason has been specified. When the environment is configured to cocumentation with reduced trust, all basic database operations require at least ReflectPermission MemberAccess and ReflectionEmit for the classes and types being persisted. When you run the query in Listing 3, the database reports three Brian s, two of them Brian Goetz.
The db4o container doesn’t run into problems of identity here because the object in question documenation already been identified as one coming from the database, meaning its OID is already stored inside the db4o bookkeeping infrastructure. Transparent Activation must be enabled in the configuration when opening a db4o database and your compiled assembly must be instrumented by Db4oTool.
Following that, I iterate through the array of objects that correspond to the values for each of those fields and then call Field. If the database is not closed cleanly, or if the application crashes at any time and dicumentation or incomplete transactions are discarded.
DefragmentConfig (db4o – database for objects – documentation)
But please don’t repeat that name to the db4o developers; you’ll get me in trouble. I then iterate through an array of Strings that have the fields in them, getting back each Field object in the Class. All field objects including collections are saved automatically. For example, it is entirely possible to write a native query complex enough to defeat the bytecode analyzer, thus requiring the worst-case execution model to take place.
For strings, matching values will contain the supplied value anywhere within the match. UpdateDepth [depth] ; The default value 1 means db4o will not descend into child objects when updating stored object instances. This, along with the emergence of a viable alternative, has led to a renaissance of interest in object persistence and retrieval. The Object Database ODB arrived in the software industry with the advent of object oriented languages.
Queries, updates, and identity
If a field in the prototype is “null,” then that value matches against any value in the data store; otherwise, the values must match exactly.
Running db4o documentagion the GAC is not supported. Because QBE uses a prototype object as its template to search for data, there are a few simple rules regarding its usage.