Java 2 Ada

Review Web Application: Listing the reviews

By stephane.carrez

After the creation and setup of the AWA project and the UML model design we have seen how to create a review for the review web application. In this new tutorial, you will understand the details to list the reviews that have been created and published. This tutorial has three steps:

  • First the definition of the database query,
  • The implementation of the Ada review list bean,
  • The writing of the XHTML facelet presentation file.

Step 1: Database query to list the reviews

Let's start with the database query that we will use to retrieve the reviews.

Since we need to access the list of reviews from the XHTML files, we will map the SQL query result to a list of Ada Beans objects. For this, an XML query mapping is created to tell how to map the SQL query result into some Ada record. The XML query mapping is then processed by Dynamo to generate the Ada Beans implementation. The XML query mapping is also read by AWA to get the SQL query to execute.

A template of the XML query mapping can be added to a project by using the dynamo add-query command. The first parameter is the module name (reviews) and the second parameter the name of the query (list). The command will generate the file db/reviews-list.xml.

dynamo add-query reviews list

The generated XML query mapping is an example of a query. You can replaced it or update it according to your needs. The first part of the XML query mapping is a class declaration that describes the type to represent each row returned by our query. Within the class, a set of property definition describes the class attributes with their type and name.

<query-mapping package='Atlas.Reviews.Models'>
    <class name="Atlas.Reviews.Models.List_Info" bean="yes">
        <comment>The list of reviews.</comment>
        <property type='Identifier' name="id">
            <comment>the review identifier.</comment>
        </property>
        <property type='String' name="title">
            <comment>the review title.</comment>
        </property>
        ...
    </class>
</query-mapping>

Following the class declaration, the query declaration describes a query by giving it a name and describing the SQL statement to execute. By having the SQL statement separate and external to the application, we can update, fix and tune the SQL without rebuilding the application. The Dynamo code generator will use the query declaration to generate a query definition that can be referenced and used from the Ada code.

The SQL statement is defined within the sql XML entity. The optional sql-count XML entity is used to associate a count query that can be used for the pagination.

We want to display the review with the author's name and email address. The list will be sorted by date to show the newest reviews first. The SQL to execute is the following:

<query-mapping package='Atlas.Reviews.Models'>
   ...
    <query name='list'>
       <comment>Get the list of reviews</comment>
       <sql>
SELECT
      r.id,
      r.title,
      r.site,
      r.create_date,
      r.allow_comments,
      r.reviewer_id,
      a.name,
      e.email,
      r.text
FROM atlas_review AS r
INNER JOIN awa_user AS a ON r.reviewer_id = a.id
INNER JOIN awa_email AS e ON a.email_id = e.id
ORDER BY r.create_date DESC
    LIMIT :first, :last
       </sql>
       <sql-count>
    SELECT
      count(r.id)
    FROM atlas_review AS r
       </sql-count>
    </query>
</query-mapping>

The query has two named parameters represented by :first and :last. These parameters allow to paginate the list of reviews.

The complete source can be seen in the file: db/reviews-list.xml.

Once the XML query is written, the Ada code is generated by Dynamo by reading the UML model and all the XML query mapping defined for the application. Dynamo merges all the definitions into the target Ada packages and generates the Ada code in the src/model directory. You can use the generate make target:

make generate

or run the following command manually:

dynamo generate db uml/atlas.zargo

From the List_Info class definition, Dynamo generates the List_Info tagged record. The record contains all the data members described in the class XML entity description. The List_Info represents one row returned by the SQL query. The attributes of the List_Info can be accessed from the XHTML files by using UEL expression and the property name defined for each attribute.

To describe the list of rows, Dynamo generates the List_Info_Beans package which instantiates the Util.Beans.Basic.Lists generic package. This provides an Ada vector for the List_Info type and an Ada bean that gives access to the list.

package Atlas.Reviews.Models is
  ...
  type List_Info is new Util.Beans.Basic.Readonly_Bean with record
  ...
   package List_Info_Beans is
      new Util.Beans.Basic.Lists (Element_Type => List_Info);
   package List_Info_Vectors renames List_Info_Beans.Vectors;
   subtype List_Info_List_Bean is List_Info_Beans.List_Bean;
   subtype List_Info_Vector is List_Info_Vectors.Vector;
   Query_List : constant ADO.Queries.Query_Definition_Access;
   ...
end Atlas.Reviews.Models;

The generated code can be seen in src/model/atlas-reviews-models.ads.

Step 2: The review list bean

In order to access the list of reviews from the XHTML facelet file, we must create an Ada bean that provides the list of reviews. This Ada bean is modelized in the UML model and we define:

  • A set of attributes to manage the review list pagination (page, page_size, count)
  • An Ada bean action that can be called from the XHTML facelet file (load)

The Review_List_Bean tagged record will hold the list of reviews for us:

package Atlas.Reviews.Beans is
  ...
   type Review_List_Bean is new Atlas.Reviews.Models.Review_List_Bean with record
      Module       : Atlas.Reviews.Modules.Review_Module_Access := null;
      Reviews      : aliased Atlas.Reviews.Models.List_Info_List_Bean;
      Reviews_Bean : Atlas.Reviews.Models.List_Info_List_Bean_Access;
   end record;
   type Review_List_Bean_Access is access all Review_List_Bean'Class;
end Atlas.Reviews.Beans;

We must now implement the Load operation that was described in the UML model and we are going to use our list query. For this, we use the ADO.Queries.Context to setup the query to retrieve the list of reviews. A call to Set_Query indicates the query that will be used. Since that query needs two parameters (first and last), we use the Bind_Param operation to give the two values. The list of reviews is then retrieved easily by calling the Atlas.Reviews.Models.List operation that was generated by Dynamo.

package body Atlas.Reviews.Beans is
...
   overriding
   procedure Load (Into    : in out Review_List_Bean;
                   Outcome : in out Ada.Strings.Unbounded.Unbounded_String) is
      Session     : ADO.Sessions.Session := Into.Module.Get_Session;
      Query       : ADO.Queries.Context;
      Count_Query : ADO.Queries.Context;
      First       : constant Natural  := (Into.Page - 1) * Into.Page_Size;
      Last        : constant Positive := First + Into.Page_Size;
   begin
      Query.Set_Query (Atlas.Reviews.Models.Query_List);
      Count_Query.Set_Count_Query (Atlas.Reviews.Models.Query_List);
      Query.Bind_Param (Name => "first", Value => First);
      Query.Bind_Param (Name => "last", Value => Last);
      Atlas.Reviews.Models.List (Into.Reviews, Session, Query);
      Into.Count := ADO.Datasets.Get_Count (Session, Count_Query);
   end Load;
end Atlas.Reviews.Beans;

Review list bean creation

The AWA framework must be able to create an instance of the Review_List_Bean type. For this, we have to declare and implement a constructor function that allocates an instance of the Review_List_Bean type and setup some pre-defined values. When the instance is returned, the list of reviews is not loaded.

package body Atlas.Reviews.Beans is
   ...
   function Create_Review_List_Bean (Module : in Atlas.Reviews.Modules.Review_Module_Access)
                                     return Util.Beans.Basic.Readonly_Bean_Access is
      Object  : constant Review_List_Bean_Access := new Review_List_Bean;
   begin
      Object.Module       := Module;
      Object.Reviews_Bean := Object.Reviews'Access;
      Object.Page_Size    := 20;
      Object.Page         := 1;
      Object.Count        := 0;
      return Object.all'Access;
   end Create_Review_List_Bean;
end Atlas.Reviews.Beans;

The constructor function is then registered in the Atlas.Reviews.Modules package within the Initialize procedure. This registration allows to give a name for this constructor function and be able to specify it in the managed-bean bean declaration.

package body Atlas.Reviews.Modules is
   ...
   overriding
   procedure Initialize (Plugin : in out Review_Module;
                         App    : in AWA.Modules.Application_Access;
                         Props  : in ASF.Applications.Config) is
   begin
      ...
      Register.Register (Plugin => Plugin,
                         Name   => "Atlas.Reviews.Beans.Review_List_Bean",
                         Handler => Atlas.Reviews.Beans.Create_Review_List_Bean'Access);
   end Initialize;
end Atlas.Reviews.Modules;

Review list bean declaration

The managed-bean XML declaration associates a name to a constructor function that will be called when the name is needed. The scope of the Ada bean is set to request so that a new instance is created for each HTTP GET request.

  <managed-bean>
    <description>The list of reviews</description>
    <managed-bean-name>reviewList</managed-bean-name>
    <managed-bean-class>Atlas.Reviews.Beans.Review_List_Bean</managed-bean-class>
    <managed-bean-scope>request</managed-bean-scope>
  </managed-bean>

Step 3: Listing the reviews: the XHTML facelet presentation file

To load the reviews to be displayed we will use a JSF 2.2 view action. The review list page has a parameter page that indicates the page number to be displayed. The f:viewParam allows to retrieve that parameter and configure the reviewList Ada bean with it. Then, the f:viewAction defines the action that will be executed after the view parameters are extracted, validated and passed to the Ada bean. In our case, we will call the load operation on our reviewList Ada bean.

<f:metadata>
    <f:viewParam id='page' value='#{reviewList.page}' required="false"/>
    <f:viewAction action="#{reviewList.load}"/>
</f:metadata>

To summarize, the reviewList Ada bean is created, then configured for the pagination and filled with the current page content by running our SQL query.

The easy part is now to render the list of reviews. The XHTML file uses the <h:list> component to iterate over the list items and render each of them. At each iteration, the <h:list> component initializes the Ada bean review to refer to the current row in the review list. We can then access each attribute defined in the XML query mapping by using the property name of that attribute. For example review.title returns the title property.

<h:list var="review" value="#{reviewList.reviews}">
    <div class='review' id="p_#{review.id}">
        <div class='review-title'>
            <h2><a href="#{review.site}">#{review.title}</a></h2>
            <ul class='review-info'>
                <li><span>By #{review.reviewer_name}</span></li>
                <li>
                    <h:outputText styleClass='review-date' value="#{review.date}" converter="dateConverter"/>
                </li>
                <h:panelGroup rendered="#{review.reviewer_id == user.id}">
                    <li>
                        <a href="#{contextPath}/reviews/edit-review.html?id=#{review.id}">#{reviewMsg.review_edit_label}</a>
                    </li>
                    <li>
                        <a href="#"
                           onclick="return ASF.OpenDialog(this, 'deleteDialog', '#{contextPath}/reviews/forms/delete-review.html?id=#{review.id}');">
                           #{reviewMsg.review_delete_label}
                        </a>
                    </li>
                </h:panelGroup>
            </ul>
        </div>
        <awa:wiki styleClass='review-text post-text' value="#{review.text}" format="dotclear"/>
    </div>
</h:list>

Understanding the request flow

Let's see the whole request flow to better understand what happens.

To display the list of reviews, the user's browser makes an HTTP GET request to the page /reviews/list.html. This page maps to the XHTML file web/reviews/list.xhtml that we created in the previous tutorial.

The Ada Server Faces framework handles the request by first reading the XHTML file and building a tree of components that represent the view to render. Within that tree of component, the <f:metadata> component allows to make a pre-initialization of components and beans before the component tree is rendered.

For the pre-initialization, the reviewList Ada bean is created because it is referenced in an EL expression used by the <f:viewParam> component or by the <f:viewAction>. For this creation, the Create_Review_List_Bean constructor that we registered is called. The page attribute is set on the reviewList Ada bean if it was passed as a URL request parameter.

The load action is then called by Ada Server Faces and the current review list page is retrieved by executing the SQL query.

As soon as the load action terminates, the rendering of the component tree can be processed. The reviewList Ada bean contains the information to display and the <h:list> component iterates over the list and renders each row at a time.

C

Conclusion

After the previous tutorial we were able to create a review and populate our database with one or several reviews. We are now able to display the list of reviews to our users.

The next tutorial will focus on using the Votes module to bring some voting capabilities in the review web application. Meanwhile, you may browse and study the sources:

db/reviews-list.xml

atlas-reviews-beans.ads

atlas-reviews-beans.adb

review-list.xhtml

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