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GemFire OQL Query

Introduction

In this lab, we will be leveraging Object Query Language (OQL) to access data within GemFire. When you are accessing data, you don’t always have the key available, nor do you know what the exact structure of the data is. In this lesson, we will be implementing methods that query GemFire data.

Concepts you will gain experience with:

  • Using a query connection in GemFire

  • Writing an OQL style query

  • Performing a query for individual attributes of an object

  • Writing queries involving joins between regions

Estimated completion time: 30 minutes

Quick Instructions

Quick instructions for this exercise have been embedded within the lab materials in the form of TODO comments. To display them, open the Tasks view (Window → Show view → Tasks (not Task List)).

Detailed Instructions

Instructions for this lab are divided into specific sections. Each section describes the steps to perform specific tasks.

Start the Back-End

For this lab, we’ll use the server-bootstrap module to start up a backend.

  1. Start the server-side processes using the server-bootstrap start.sh script (start.bat for Windows) inside the folder cluster:

    cd server-bootstrap/cluster
./start.sh

  2. Next, run the gradle task 'seedRegions' to seed the regions with some data

    cd server-bootstrap
gradle seedRegions

Implementing the general query functionality

To start, you will implement a general purpose query method, doQuery() that simply takes a String as an argument and returns a SelectResults result set. While not robust enough for broad usage, it will suit the purpose for this lab to have this functionality encapsulated in a method such that the remaining sections can focus primarily on writing the query string.

(TODO-01) Open the OQLInquirer.java class file (in the io.pivotal.bookshop.buslogic package) and locate the doQuery() method, which has been stubbed out for you. Implement the functionality of this method to perform the following tasks:

  • Get a QueryService from the cache

  • Create a new query using the supplied query string

  • Execute the query, which will have to be done inside a try/catch block

  • Either return the results of executing the query or throw a QueryException wrapping an exceptions caught in the catch block

Basic OQL Query with Objects

This section will do a query against the Customer region to access data as Customer Objects.

  1. Open the test OqlInquirerTests.java in the io.pivotal.bookshop.tests package. Execute the test named testBasicQuery(). It should fail.

  2. (TODO-02) Back in the class OqlInquirer, locate and implement the doCustomerQuery() method. You will only need to:

    1. Write a proper OQL query in the query string to fetch all entries from the Customer region

    2. Return the results of calling the doQuery() method with the query string you just wrote

  3. (TODO-03) Re-run the test testBasicQuery(). If you correctly implemented the doCustomerQuery() method in the prior step, it should now pass.

    Note
    		 Don’t worry yet that the other two tests are failing. You will fix this in the remaining sections.

OQL Query with Struct objects

Once you have the basic customer query working, let’s move on to write a similar query to only return certain fields of the Customer object.

  1. Run the test named testStructQuery() and watch it fail

  2. (TODO-04) Locate the doStructQuery() method in the OQLInquirer class. Implement the method as follows:

    1. First, write the correct query string to return a projection list. That is, perform a query where you will return only the customerNumber, firstName and lastName fields of the Customer entries.

    2. Return the results of calling doQuery() with the query string you just wrote

  3. (TODO-05) Return to the OqlInquirerTests class and re-run the test to verify you correctly implemented this functionality. If so, then testStructQuery() should now pass.

Performing Joins

In this final section, you will be creating a more complex query by performing a join operation between the Customer region and BookOrder region. The goal is to return a list of all customers who have placed an order with total price greater than $45.00. To better understand the requirements for this query, take a moment to examine the following diagram showing the class definitions found within these two regions.

Join Query

You will be performing an equi-join query in which you link Customer entries in the /Customer region to the BookOrder entries in the /BookOrder region by the customerNumber property of each object. With this in mind, perform the following tasks.

  1. Run the test named testJoinQuery() and watch it fail.

  2. (TODO-06) Locate the doJoin() method in the OQLInquirer class. Implement the method as follows:

    1. First write the correct query string to perform the join query. You are selecting a unique list of customers who’s total order is greater than $45.00.

    2. Return the results of calling doQuery() with the query string - you should be returning a SelectResults for Customer objects.

  3. (TODO-07) Return to the OqlInquirerTests class and re-run the tests to verify you correctly implemented the join query functionality. If so, then all 3 tests should now pass.

Congratulations!! You have completed this lab.