Expressions#

Query arguments are written as expressions compiled at startup using expr-lang/expr. Each expression has access to the built-in functions, globals, and any user-defined expressions.

Tip: Use edg repl to try any expression interactively without a database connection. See REPL for details.

Functions#

These are edg’s built-in functions, available in any expression context (args:, expressions:, globals). They generate data, reference datasets, aggregate values, and control execution flow.

Choosing a Sequence Generator#

edg has three ways to generate sequential IDs. Picking the wrong one silently produces incorrect data, so choose carefully.

Common mistakes#

Don’t use seq() across multiple seed queries.

seq(1, 1) is a single counter that never resets. If populate_accounts uses seq(1, 1) with count: 10, the counter reaches 10. A later populate_counters query using the same seq(1, 1) continues from 11, not 1. Use iter() instead - it resets per batch query.

seed {
  populate_accounts(count: 10)
    `INSERT INTO account (id) VALUES ($1)` (seq(1, 1))

  populate_counters(count: 10)
    `INSERT INTO counter (id) VALUES ($1)` (seq(1, 1))
}

seed:
  - name: populate_accounts
    type: exec_batch
    count: 10
    args:
      - seq(1, 1)        # 1..10
    query: INSERT INTO account (id) VALUES ($1)

  - name: populate_counters
    type: exec_batch
    count: 10
    args:
      - seq(1, 1)        # 11..20
    query: INSERT INTO counter (id) VALUES ($1)

seed {
  populate_accounts(count: 10)
    `INSERT INTO account (id) VALUES ($1)` (iter())

  populate_counters(count: 10)
    `INSERT INTO counter (id) VALUES ($1)` (iter())
}

seed:
  - name: populate_accounts
    type: exec_batch
    count: 10
    args:
      - iter()           # 1..10
    query: INSERT INTO account (id) VALUES ($1)

  - name: populate_counters
    type: exec_batch
    count: 10
    args:
      - iter()           # 1..10
    query: INSERT INTO counter (id) VALUES ($1)

Don’t use seq() when you need globally unique IDs.

With multiple workers, each worker’s seq(1, 1) produces 1, 2, 3, … independently - you’ll get duplicate IDs. Use seq_global instead.

Don’t use seq_global() for seed queries.

The counter never resets, so re-running deseed + seed produces new IDs each time. Use iter() for seeds and reserve seq_global for run workloads.

Function Lifecycle#

Several functions maintain state. Understanding when that state resets is important for getting correct results: