Difference between revisions of "DTO DSL"

Revision as of 12:54, 4 August 2016

Copyright Notice

All rights are reserved by Compex Systemhaus GmbH. In particular, duplications, translations, microfilming, saving and processing in electronic systems are protected by copyright. Use of this manual is only authorized with the permission of Compex Systemhaus GmbH. Infringements of the law shall be punished in accordance with civil and penal laws. We have taken utmost care in putting together texts and images. Nevertheless, the possibility of errors cannot be completely ruled out. The Figures and information in this manual are only given as approximations unless expressly indicated as binding. Amendments to the manual due to amendments to the standard software remain reserved. Please note that the latest amendments to the manual can be accessed through our helpdesk at any time. The contractually agreed regulations of the licensing and maintenance of the standard software shall apply with regard to liability for any errors in the documentation. Guarantees, particularly guarantees of quality or durability can only be assumed for the manual insofar as its quality or durability are expressly stipulated as guaranteed. If you would like to make a suggestion, the Compex Team would be very pleased to hear from you.

(c) 2016-2024 Compex Systemhaus GmbH

Purpose

The DTO DSL facilitates the creation and handling of data transfer objects (DTOs) in order to carry data between processes. Communication between processes is usually done by calls to remote interfaces and services where each call is a computationally expensive and time-consuming operation. The use of DTOs that aggregate the data that would have been transferred separately reduces the number of calls that are necessary, thus speeding up the operation. Furthermore, DTOs are decoupled from the JPA, thus eliminating burdensome dependencies.

Using the DTO DSL, it is easy to create DTOs and the mapper classes that link them to the respective persistence entities. Property change support is automatically included in order to have current data without direct dependencies on the persistence layer.

Overview

The main semantic elements of the DTO DSL are the following:

• Package - the root element that contains all the other elements. A model can contain multiple packages.
• Import declarations - used to import other DTO models or the entity model files that are covered by the DTOs.
• Datatype declarations - a way to define datatypes that can be used (only within the package - private scope).
• DTO - the model of a DTO that wraps an entity. It contains further elements such as properties and references. Appropriate mapper methods can be specified.
• Property - a reference to an enum, a Java class or a “simple datatype" (as defined in the datatype declaration). Can be inherited from the wrapped entity and offers multiplicity.
• Reference - a reference to another DTO. Can be inherited from the wrapped entity and offers multiplicity.
• Operations - similar to Java methods. The Xbase expression language can be used to write high-level code.
• Comments can be added to all elements.

► Caveat: In order to make use of the DTO DSL, one has to make sure that the OSBP builder is executed after the Xtext builder.

DTO model files

DTO models are described in .dtos files. These files describe the DTO model and are the basis for the code generation. DTO models may be split over several .dtos files containing packages in the same namespace.

A .dtos file may contain several packages with DTOs.

package

Packages are the root element of the DTO DSL grammar. Everything is contained in a package: Imports, datatypes, DTOs and enums have to be defined inside the package definition. One document can contain multiple packages with unique names.

The elements a package can contain are DTOs and enums. Additionally, a package allows import statements and the declaration of datatypes.

► Syntax:

 package name {
    import importStatement;
    datatype datatypeDefinition;
    DTOs
 }

Figure 1 - DTO model file - a package is the topmost element and contains other items.

import

In order to wrap entities into DTOs, the DTO DSL has to reference entities defined in entity model files. Furthermore, it is possible to reference DTOs in other packages. The import statement is a way to address these elements by their fully qualified name.

Import statements allow the use of the *-wildcard.

► Syntax:

package name {
    import importStatement;
    datatype datatypeDefinition;
    DTOs
}

Figure 2 - Items contained in another package can be accessed and handled if the package is imported.

datatype

The DTO DSL allows the definition of datatypes. These are translated by the inferrer into their standard Java presentation. The behaviour of the generator can be controlled by the datatype definitions. There are three types of datatype definitions:

jvmTypes

Datatpye definitons that map types to jvmTypes take the basic syntax of
datatype <name> jvmType <type> as primitive;
Specifying datatypes in this manner uses an appropriate wrapper class in the generated Java code; adding the keyword as primitive enforces the use of primitive datatypes where applicable:
datatype foo jvmType Integer compiles to an Integer whereas
datatype foo jvmType Integer as primitive results in int.

dateTypes

The datatypes for handling temporal information can be defined by the following statement:
datatype <name> datetype date|time|timestamp;
Datatypes that have been defined in this manner can be used as property variables in DTOs.

blobs

Binary blobs can be handled by defining a datatype with the as blob keyword. The Java implementation of such a blob is a byte array.
datatype <name> as blob;

After import statements and datatype definitions, the content of the .dtos file is made up of DTO definitions.

DTO

Data Type Objects (DTO) are the most complex elements in the DTO DSL. A DTO wraps an entity defined in the Entity DSL and its properties and references into a single object used for communication purposes.

DTO are defined by name, properties, references and wrapper methods. A DTO normally does not implement business logic.

For each DTO that is defined in a package, the DTO DSL automatically generates a Java DTO class and a corresponding mapper class that handles data transfer and conversion between DTO and entity.

► Syntax:

abstract dto <name> extends <parentDto> wraps <entityName> {
    dtoFeatures
}

Figure 3 - The defined DTO is translated to a Java class and an appropriate mapper class.

extends

extends marks a DTO that is derived from another DTO. That means that the properties and references of the parent DTO are inherited.

File:Dto-04.png

Figure 4 - The extends keyword causes a Java subclass to be created for the DTO.

wraps

wraps indicates the entity that is handled by the DTO. The entity has to be imported from the entity model file into the DTO package (for importing several entities, the use of the _*_-wildcard may be advisable).

Figure 4 - The wraps keyword links the DTO to its respective entity. Thus, properties and references of the entity are made available in the DTO (and can there be accessed via content assist).

Enums

Enums are an abstraction above the Java enum. They compile to enum classes and can be used as properties in DTOs.

Figure 6 - Defining enums allows using them as variables in DTOs.

Properties

Properties of DTOs are references to datatypes or enums. They can be regarded as variables and are defined by a keyword followed by a datatype (Java type or datatype defined in the datatype section) and a name.

Properties can be determined with the following keywords:

var

The basic property. Defines a variable that can be used within the DTO. Appropriate getters and setters are created.

Figure 7 - Variables can be defined using the var keyword.

id

► -- deprecated -- deprecated -- deprecated -- deprecated -- deprecated -- deprecated -- deprecated -- deprecated --

defines a field in the DTO for mapping an id property (used as primary key in the persistence layer). This keyword is deprecated. If no id is given, a warning is shown. Caution: ID autogeneration causes problems since the value is not set before the entity is persisted in the database, which can cause problems.

It is advised to use the uuid keyword instead.

Figure 8 - Variables can be defined using the var keyword.

uuid

creates a field for the mapping of Universally Unique IDs as primary keys. UUIDs have to be strings.

Figure 9 - By using the uuid keyword, eliablyunique IDs can be used as primary keys and mapped to a DTO.

version

defines a field for mapping a version property used by the JPA-Compiler.

Figure 10 - A version property can be mapped into a DTO by the version keyword.

transient

marks the property to be transient. Transient properties are not mapped from the DTO to the entity and thus not persisted. Getter and setter methods are created.

Figure 11 - The transient keyword allows properties to be excluded from the mapping.