Building blocks of apps built with structrAnatomy of a Structr App

This chapter answers the following questions:

The building blocks

A Structr app has a data model, a user interface, and processes that implement the business logic of the application. Together with pre-configured building blocks to reduce the need for boilerplate code, this is what makes an application:

You build
  • dynamic HTML pages
  • data objects with attributes, and relationships between them
  • object methods, flows or scripts
Structr provides
  • data access via REST endpoints
  • integrated authentication and access control
  • a filesystem to store documents, images and resources
  • large scripting library
  • predefined object types to use and extend

User Interface

The user interface of a Structr App consists of Structr pages that are served by the built-in HTTP server (Jetty) under a specific URL. To access the application, you simply point your browser to the location of your Structr server, which is usually at http://localhost:8082/structr if Structr is running.

How do I build the user interface?

To manage the user interface, Structr provides a visual web application builder. With the builder, you can either import HTML application templates or individual pages from a URL, or create everything from scratch. The resources (like CSS files, Javascript files, or images etc.) are downloaded automatically and stored in the Structr Filesystem, protected by the same access control and authentication layers as the rest of the data.

What is a page?

A Structr page is a tree-like structure of nested HTML elements, stored in the graph database, so the representation in the database corresponds exactly to the structure of the HTML output. In the rendering process, a page behaves like a declarative “program” that combines context information, access control and script expressions to create a dynamic HTML document.

Data Model

The Data Model controls how data is stored in the database, which fields are present in the REST endpoints, how the REST endpoints behave, and much more. The data model contains all information about the data types (or classes), their properties and how the objects are related, as well as their methods.

How does it work?

Like all other application components, the data model is stored in the graph database and can be modified and extended at any time. After the system has been started or when changes have been made, Structr translates the schema entities into Java source code which is then compiled into Java classes that implement the functionality of the application.

What about data validation?

For each data type you can specify simple constraints based on attribute values (e.g. mandatory fields), detailed consistency checks and lifecycle methods that trigger event-driven processes (e.g. send an e-mail when a document is available for review) or automated workflows (BPMN).

Based on the schema details, Structr validates the integrity and structure of the data in the system when data is sent or received through REST endpoints. Structr generates meaningful semantic error messages, e.g. if constraints are violated or the input does not comply to the integrity and structure rules defined for a certain data type.

Business Logic

Most of the processes in Structr are event-driven: things happen when database objects are created, modified or deleted. For these events, Structr provides lifecycle methods that you can implement on any type in the data model (even the built-in types), using either StructrScript or Javascript.

More

In addition to the lifecycle methods, you can of course add arbitrary methods to any type, and execute them via REST or from other scripts.

The third option to implement logic is to use a global schema method, especially when the logic is not bound to a specific type. Global schema methods can be called via REST using a special maintenance endpoint, scheduled for execution with a cron-like syntax or called from any scripting envrionment using the call() or call_privileged() functions.

Security

Structr provides integrated multi-level access control for all parts of the application based on user and group objects. Both the access to the data and the representation of individual areas of the web application can be controlled separately with different security models.

Access to the REST endpoints can even be controlled for each HTTP verb separately.

Accessing the Data

Structr automatically creates REST endpoints from the data model that allow you to read and write data as JSON documents. You can send a JSON document to an endpoint, and Structr automatically creates the corresponding object structure in the database, based on the schema definition in the data model. This works in both directions, so Structr is essentially a document database extension on a graph database.

Please refer to the REST Guide to learn more about the REST interface and its features.

Other interfaces

Various interfaces are available for integrating a Structr application into a company’s IT landscape, ranging from data import tools for RDF, CSV, XML and SQL to interactive technologies such as SSH and FTP to automated processing of mass data via the REST interface. In addition, ActiveDirectory support exists, and it is also possible to connect e-mail mailboxes via SMTP.