تحرير

مشاركة عبر

Get latest versions of Azure Cosmos DB documents

  • مقالة

In this article, you'll learn how to get the latest version of ingested documents.

Get the latest versions of documents

Every time a document update is ingested from the change feed, a new row is added in the target table. Over time, the table builds up a history of every document in the corresponding Cosmos DB container. A typical requirement is to query the latest version of a document, corresponds to getting the current state of the Cosmos DB container.

You can use the following ways to query the current state from your table:

In the examples, you'll get the latest versions of the document by summarizing the table by the Id column, using the arg_max function on the _timestamp column to only show the rows with the most recent timestamps.

Note

The _timestamp column is created from the _ts property of ingested the Cosmos DB documents. The conversion from DateTimeFromUnixSeconds (_ts) to datetime (_timestamp) is performed by the ingestion table mapping configured for the table. The converted data in the _timestamp column makes queries and materialized views more performant than using the native DateTimeFromUnixSeconds _ts value.

Run a query to get the latest versions of documents

Run the following query to get the latest versions of documents:

TestTable
| summarize arg_max(_timestamp, *) by Id

If you used soft markers to mark deleted documents, you can filter them out with the following query:

TestTable
| summarize arg_max(_timestamp, *) by Id
| where not(IsDeleted)

Create a materialized view of the latest versions of documents

If your Cosmos DB container has a lot of updates, the query to get the latest versions of documents can be slow. Materialized views usually have better performance than a query if there are a lot of updates. If the query is frequently run, using a materialized view can be beneficial and save cost.

Run the following command to create a materialized view of the latest versions of documents:

.create materialized-view LatestDocuments on table TestTable
{
    CosmosChangeFeed1
    | summarize arg_max(_timestamp, *) by Id
}

In a materialized view, you can't filter our soft markers as part of its query. Therefore, to remove deleted documents indicated by soft markers, query the materialized view and filter the results, as follows:

LatestDocuments
| where not(IsDeleted)

Optionally, encapsulate the filtered query in a stored function and call it to get the latest filtered results, as follows:

.create function LatestDocumentsDeletedRemoved(){
    LatestDocuments
    | where not(IsDeleted)
}

LatestDocumentsDeletedRemoved
| summarize sum(Salary) by Area

Related content