Is it possible to JOIN two different data sources in couchbase mobile?

Mobile
1

I have created two different databases in mobile. I want to join them. How to do that?
Database 1, name = employee
Sample document: {
“name”: “Employee 1”,
“email”: "employee1@org.com",
“department”: “department-01”
}

Database 2, name = department
{
“name”: “Department 01”,
“id”: “department-01”
}

Desired output: {
“name”: “Employee 1”,
“email”: "employee1@org.com",
“departmentName”: “Department 01”
}

2

I have not tried this myself yet. Have you tried setting both databases as the sources in the JOIN part of your query?

3

Yes. Here is the sample query (in Android Java).

    DataSource departmentDS = DataSource.database(departmentDatabase).as("departmentDS");
    DataSource employeeDS = DataSource.database(employeeDatabase).as("employeeDS");

    Expression employeeDeptExpr = Expression.property("department").from("employeeDS");

    Expression departmentCodeExpr = Expression.property("id").from("departmentDS");

    Expression joinExpr = employeeDeptExpr.equalTo(departmentCodeExpr);

    Join join = Join.join(departmentDS).on(joinExpr);
    Query searchquery = QueryBuilder.select(
        SelectResult.expression(Expression.property("name").from("employeeDS")),
        SelectResult.expression(Expression.property("email").from("employeeDS")),
        SelectResult.expression(Expression.property("name").from("departmentDS")))
        .from(employeeDS)
        .join(join);

ResultSet rs = query.execute();
List resultList = rs.allResults();

resultList.size(); // is giving zero

4

No, we do not support cross database joins at this time. Is there a reason you have your documents in two different databases ?

5

What Priya said. In CBL you generally put related data in the same database.

6

I am using separate buckets for sync-able and local data which helps me in reducing the code complexity for better design.

7

Thats a good pattern for segregating local-only and sync-able data. However, if you need to do queries that span across databases then at this time, the recommended pattern would be to have a single database and to set up replication filters to filter out the local-only data.