[CALCITE-4311] Add non-nullable experimental accessors side by side with their nullable counterparts

• Type: Sub-task
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 1.25.0
• Assignee: Unassigned
• Reporter: Vladimir Sitnikov
• Created: 05/Oct/20 14:01
• Updated: 07/Oct/20 21:49

Description

Certain APIs are declared to return nullable values, however, they are often used in "I know this must be non-null" context.

For instance: Wrapper#unwrap(Class).
It happens so that .unwrap(Table.class) is quite common.
For instance:

            final Table leftTable = leftRelOptTable.unwrap(Table.class);
            final int leftCount = leftRelOptTable.getRowType().getFieldCount();

It would be nice if unwrap could fail with a proper message like "oh, I can't find Table in ...", so the end users would get better error messages, and the code would be way easier to read.

For instance:

// unwrapNonNull can be declared as a default implementation
            final Table leftTable = leftRelOptTable.unwrapOrThrow(Table.class);
            final int leftCount = leftRelOptTable.getRowType().getFieldCount();

—

Another case is org.apache.calcite.sql.SqlSelect#getSelectList. The method returns a nullable value, however, it is often used as if it was non-nullable.

Initially, I thought of adding static helper methods to utility classes/interfaces, however, now I'm inlined to adding non-nullable getters right to the original classes/interfaces.
That would make the code easier to read and write.

—

Another quite common case is metadata: sometimes users need non-null value for the metadata, so it would be nice to have a default value via argument or throw in case of missing metadata.
See CALCITE-4215