Table Store (aka ORM) Package

[aaronc]

This is linked to meta-issue #7096.

Summary

This issue proposes a new table-store package which allows for automatic secondary index creation. The code for this already exists here: https://github.com/regen-network/cosmos-modules/tree/master/incubator/orm but it is not part of the SDK.

Problem Definition

Oftentimes modules want to create secondary indexes for data being stored. A good example is x/staking (see x/staking/types/keys.go). As can be seen in the x/staking example, it is fairly complex to do this manually.

Proposal

The table-store package would provide a framework for creating effectively database tables with primary and secondary keys.

The current implementation of this is called orm (for object-relational mapping), but a more correct name is likely table-store. Instead of a key-value store, we actually have a relational database table store.

Currently this implementation has support for:

• auto-incrementing uint64 primary keys
• natural primary keys
• uint64 secondary indexes
• []byte secondary indexes
• multi-key secondary indexes

More functionality could be added as needed.

This is related to the proposed schema module (see #7097). The table-store module would automatically generate schema descriptors for registered tables whereas existing modules would need to create those schemas manually.