Substreams Sink Database Changes

substreams-sink-database-changes contains all the definitions for database changes which can be emitted by a substream.

To be consumed by

• substreams-sink-sql

Install

# The Rust crate is named substreams-database-change for historical reasons
cargo add substreams-database-change

Quickstart

Cargo.toml

[dependencies]
substreams = "0.6"
substreams-database-change = "2.0"

src/lib.rs

use substreams::errors::Error;
use substreams_database_change::tables::Tables;
use substreams_database_change::pb::database::DatabaseChanges;

#[substreams::handlers::map]
fn db_out(
    ... some stores ...
) -> Result<DatabaseChanges, Error> {
    let mut tables = Tables::new();

    // Create a row and set fields
    tables
        .create_row("transfer", "some-id")
        .set("key1", "value1")
        .set("key2", "value2");

    // Update a row (for example, change key2)
    tables
        .update_row("transfer", "some-id")
        .set("key2", "new_value2");

    Ok(tables.to_database_changes())
}

Reference

Table Operations

• Create a row

  tables.create_row("table_name", "primary_key")
      .set("field", "value");

  Creates a new row. Panics if the row is already scheduled for upsert, update, or delete.

• Upsert a row

  tables.upsert_row("table_name", "primary_key")
      .set("field", "value");

  Schedules an insert or update (upsert) for the row. Panics if the row is already scheduled for create, update, or delete.

• Update a row

  tables.update_row("table_name", "primary_key")
      .set("field", "new_value");

  Schedules an update for the row. Panics if the row is already scheduled for delete.

• Delete a row

  tables.delete_row("table_name", "primary_key");

  Schedules a delete for the row. Clears any previously set fields.

All methods support both single and composite primary keys:

tables.create_row("table", [("key1", "v1".to_string()), ("key2", "v2".to_string())]);

Automatic Type Transformations

The .set() method automatically converts many Rust types to database-compatible strings, including:

• Integers: i8, i16, i32, i64, u8, u16, u32, u64
• bool
• String, &str
• BigInt, BigDecimal (from substreams::scalar)
• prost_types::Timestamp
• Vec<u8>, Hex<T> (as hex strings)

Custom types can implement the ToDatabaseValue trait for custom conversion.

For advanced use, .set_raw() allows setting a field to a raw string value.

Re-generate Protobuf

Be sure to have buf CLI installed (https://buf.build/docs/installation/) and run:

buf generate proto

Release

sfreleaser release

Follow instructions the CLI is asking, the process is now automatic and version bump and Substreams package building is now all done automatically.