Aerospike secondery index on map

Question

I have a question about Aerospike DB , and secondry indexes.

I have set of students , and each student (record key is StudentId), has a map (bin) , that consists of <CourseId ,Grade>.

I want to select only students that participated specific coursesIds . How can I do it ? Should I add secondry index on the map? Using UDF?

Thanks.

Answer 1

You could use two approaches - one with secondary indexes, and one without (just key-value operations using the primary index).

Without Secondary Indexes

Let's actually assume you have three types at your application, each in its own set in Aerospike - courses, students, roster. The course object holds information about the course, the student objects hold information about the student. The roster objects have the same key as the course, or maybe a composite courseID|semester. The course should have a bin students which holds a list of student IDs. To get the students of a course you get the roster record, then turn its list of student keys into a single batch-read operation against students.

Of course you could also collapse this and just have two sets - courses and students and keep the list of course students as a bin in the course object. No need for a many-to-one join here, since you have the list and map complex data types to work with.

If you wanted to do more complex queries without a secondary index, you can apply a predicate filter onto a scan of the courses set (See an example of using the Java client this way).

With Secondary Indexes

You can add a bin in-course to the student objects, with its value being a list of course IDs (meaning that you can easily get the course object from the ID). You can build a secondary index over that list of course IDs. To get the student's courses you get the student object by its key, and look at the in-course bin. To get all the students in a specific course, run a secondary index query over that bin of the records in the students set.

You can apply a predicate filter to the records found by this secondary index query, to further filter the students by other criteria.