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Feature 98: Loading data objects from server with an SQL query
April 16, 2015 by markpiller
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Previously I have reviewed multiple techniques for loading data objects from the persistent server-side storage. There is a list of all articles categorized by topic. In this post I am going to review the API for loading data objects using an SQL query. I already wrote once about SQL queries in Backendless and that post described how to test queries using console. I recommend reading that post before reviewing the samples below.

Consider the following data tables:

There are 2 Person objects:
person objects - Feature 98: Loading data objects from server with an SQL query

And there are 3 Address objects. Notice there is a one-to-many relation between Person and Address objects:
address objects - Feature 98: Loading data objects from server with an SQL query

Suppose you need to load all persons who are older than 21 and live in New York city. The following query expresses exactly that condition:

Notice the query references object properties/columns to define the search expression. The addresses column in the Person table references a collection of the Address objects. Since Address has the city column, it is identified using the dot notation in the query.

The code below demonstrates the query in action:

Asynchronous API sample (Android and Plain Java):

Synchronous API sample (Plain Java only):

Program output:

The API is designed in a way that let’s you combine query-based search with sorting, loading of relations, paging and many other data search-related features of Backendless.

 

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