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50 lines
2.6 KiB
Plaintext
50 lines
2.6 KiB
Plaintext
[#QInstance]
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== QInstance
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include::../variables.adoc[]
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An application in QQQ is defined as a set of Meta Data objects. These objects are all stored together in an object called a `*QInstance*`.
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Currently, a `QInstance` must be programmatically constructed in java code - e.g., by constructing objects which get added to the QInstance, for example:
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[source,java]
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.Adding meta-data for two tables and one process to a QInstance
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----
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QInstance qInstance = new QInstance();
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qInstance.addTable(definePersonTable());
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qInstance.addTable(defineHomeTable());
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qInstance.addProcess(defineSendPersonHomeProcess());
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----
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It is on the QQQ roadmap to allow meta-data to be defined in a non-programmatic way, for example, in YAML or JSON files, or even from a dynamic data source (e.g. a document or relational database).
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The middleware and/or frontends being used in an application will drive how the `QInstance` is connected to the running server/process.
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For example, using the `qqq-middleware-javalin` module, a the `QJavalinImplementation` class () has a constructor which takes a `QInstance` as an argument:
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[source,java]
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.Starting a QQQ Javalin middleware server - passing a QInstance as a parameter to the new QJavalinImplementation
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----
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QJavalinImplementation qJavalinImplementation = new QJavalinImplementation(qInstance);
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Javalin service = Javalin.create();
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service.routes(qJavalinImplementation.getRoutes());
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service.start();
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----
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*QInstance Setup:*
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These are the methods that one is most likely to use when setting up (defining) a `QInstance` object:
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* `add(TopLevelMetaDataInterface metaData)` - Generic method that takes most of the meta-data subtypes that can be added
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to an instance, such as `QBackendMetaData`, `QTableMetaData`, `QProcessMetaData`, etc.
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There are also type-specific methods (e.g., `addTable`, `addProcess`, etc), which one can call instead - this would just
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be a matter of personal preference.
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*QInstance Usage:*
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Generally you will set up a `QInstance` in your application's startup flow, and then place it in the server (e.g., javalin).
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But, if, during application-code runtime, you need access to any of the meta-data in the instance, you access it
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via the `QContext` object's static `getInstance()` method. This can be useful, for example, to get a list of the defined
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tables in the application, or fields in a table, or details about a field, etc.
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It is generally considered risky and/or not a good idea at all to modify the `QInstance` after it has been validated and
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a server is running. Future versions of QQQ may in fact restrict modifications to the instance after validation.
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