- Java annotations database schema update#
- Java annotations database schema software#
- Java annotations database schema code#
The first step is to define a database via class declarations in a Java application.
Annotations can be obtained using the reflection API at runtime. The default "value" parameter can be set without specifying the name of the parameter Annotations’ parameters can be specified using keyword notation, and if a parameter is not specified, then a default value is used. Annotations can be associated with types, fields, methods, parameters and local variable declarations. Annotations are represented with syntax in which the annotation’s name is preceded by the character. Annotations are a special kind of Java interface. For this article it is enough to know that Complete information about annotation syntax and semantics in Java can be found at. As an example it uses the Java Native interface (JNI) for the eXtremeDB embedded database, which provides a means for this database system written in C to be used from within “pure” Java applications. The remainder of this article illustrates how Java’s annotations and reflection can be harnessed to provide a database API that is both easier to use, and less error-prone, than alternative approaches. Presenting an Annotations-Based DBMS Interface in Java 
Java annotations database schema software#
Require the programmer to describe class formats - in which case this work may actually be done twice: once when declaring the classes in the application, and a second time, when describing their format for the DBMSīut in Java, reflection can enable the DBMS to get format information about application classes at runtime, eliminating the need for either extra software (the specialized compiler or preprocessor) or extra work. Use a specialized compiler or preprocessor that analyzes application source and extracts class information, or. In languages such as C/C++ there are two common ways to do this: Since Java works with objects, one requirement is to specify the format of objects (classes) to the database engine. Also, to query the database efficiently, indexes must be created, and there should be a way for the programmer to mark primary and foreign keys within the Java class.Īnnotations are especially powerful as the basis for a DBMS interface when combined with Java’s reflection mechanism, which allows an application to get information about class format at runtime. For example, a string field can be stored in a database using different encodings. This is especially beneficial in a database interface because object descriptions are necessarily complex: a database needs more information than is available in a normal Java class definition. By centralizing information about object formats, annotations simplify the programmer’s job, and eliminate the risk of errors from discrepancies in the way objects (classes) are described. 
While not yet widely recognized, annotations have a highly useful role in developing an interface to a database management system. With annotations, this information can be accessed in one location for learning, updates, etc.
Java annotations database schema update#
And while a discrepancy between implementation and documentation is bad but not critical, inconsistency in other areas can be fatal, such as when a configuration file explains the format of a class, and then a new field is added to this class without an update to the configuration file. This is inconvenient, but what’s worse is that the information in separate places soon becomes inconsistent: for example, the program sources are updated but not the documentation. But these are explained in the documentation file, which then must be opened and searched. When looking at the source of a method, the developer may want to understand the meaning of its parameters. The problem with this approach lies in the difficulty collecting and managing (programmatically as well as mentally) all the necessary information.
Java annotations database schema code#
Consider the "classical" approach: there are source files with program code separate files with API documentation that describes the behavior of this code and additional files in SQL or some other format providing some related information (needed, for example, for a database interface). The main idea of annotations is to give the programmer the ability to specify all necessary information in the same place. Annotations are a Java feature introduced in JDK5 (a similar mechanism, attributes, also exists in.
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