Developer checkpoint

Why can a subgraph mapping not call an external API?

Determinism is what makes indexers' proofs comparable. It also matters that an external service is a trust assumption nobody in the protocol can audit, in a system whose purpose is not having one.

You publish a subgraph. Nothing indexes it. Why?

Publishing makes service possible rather than guaranteed. Signal is what makes your subgraph worth an indexer's stake, which is why the docs suggest developers curate their own.

Which schema change is safe for existing consumers?

Adding is safe. The others break queries you cannot see, and consumers query a specific deployment rather than following your latest version.

Your application needs token balances across four chains, this week. Best choice?

That is exactly the repeated question the Token API absorbs. Authoring four subgraphs to answer a solved question costs weeks and consumes indexing capacity re-deriving data somebody already derived.

A query returns an empty array. What should your application do?

None of the three errors. Absent data rendering as a healthy empty state is one of the most persistent bugs in applications built on indexed data, precisely because nothing goes wrong visibly.

Which is the strongest reason NOT to use Substreams?

The parallelism solves a problem you do not have, and a module one person understands is a liability when that person is away. A maintainable subgraph beats an unmaintainable pipeline.