Gerador de upsert

Upsert no Amazon DynamoDB: PutItem with ConditionExpression

Nomeie tabela, chave e colunas e receba a instrução que o Amazon DynamoDB realmente aceita, com uma guarda para que uma linha antiga nunca sobrescreva uma nova. Abaixo: como a mecânica funciona, o que quebra e como a Datrise carrega o Amazon DynamoDB de forma incremental.

As notas técnicas desta página estão em inglês.

Gere a instrução

Instrução · PutItem with ConditionExpression

import { DynamoDBDocumentClient, PutCommand } from "@aws-sdk/lib-dynamodb";

// item: { id, name, stage, amount, owner_id, updated_at }
async function upsert(ddb, item) {
  try {
    await ddb.send(new PutCommand({
      TableName: "deals",
      Item: item,
      ConditionExpression: "attribute_not_exists(#pk) OR #wm < :wm",
      ExpressionAttributeNames: { "#pk": "id", "#wm": "updated_at" },
      ExpressionAttributeValues: { ":wm": item.updated_at },
    }));
  } catch (err) {
    if (err.name !== "ConditionalCheckFailedException") throw err;
    // stale version: a newer item is already stored, skip it
  }
}

Como o upsert funciona no Amazon DynamoDB

DynamoDB has PutItem, which writes the whole item, and UpdateItem, which edits attributes; neither is an upsert until you add a ConditionExpression. The generated code writes the item only when the key does not exist yet or the stored updated_at is older, and treats ConditionalCheckFailedException as "stale, skip". That gives you a watermark upsert with one request per item.

Batching changes the trade-off. BatchWriteItem takes 25 items but cannot carry a condition, so it is last-write-wins; TransactWriteItems takes 100 conditional writes at twice the cost. Design the partition key from the entity id so writes spread evenly, and keep items small: write capacity is billed per 1 KB, and a nested CRM record with long text lists can cost several units per upsert.

Antes de executar

PutItem replaces the whole item. Use UpdateItem with SET expressions when the source sends partial records, or attributes the source stopped sending will vanish.
BatchWriteItem (25 items) cannot carry a ConditionExpression; TransactWriteItems (100 items) can, at twice the write cost. For plain last-write-wins, batch; for the watermark guard, transact or loop.
Write capacity is billed per 1 KB of item size, rounded up. A wide CRM record with nested lists costs several WCUs per upsert; trim it before the write, not after.

Perguntas frequentes

PutItem or UpdateItem for a sync?

PutItem when the staged item is complete. UpdateItem with SET when the source sends partial records, otherwise attributes it omitted are erased.

Can BatchWriteItem apply the updated_at guard?

No. Batch writes are unconditional. Use TransactWriteItems for conditional batches, or accept last-write-wins and dedupe the batch by key before sending.

How do I handle a hot partition during backfill?

Backfills hit many keys at once, which is fine when the partition key is the entity id. Problems come from a low-cardinality key such as account_id; add the entity id to the key or use a sort key.

O mesmo gerador para outros destinos

Pule a escrita do merge

A Datrise entrega entidades de CRM e SaaS no Amazon DynamoDB com exatamente esta mecânica, uma marca d'água sobre updated-at e colunas tipadas, então a instrução acima é a que roda por você. Entre na lista de espera para acesso antecipado.

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