Querying: HTTP (Legacy)
This article provides an overview on how to perform read operations in Ditto, including how to construct your queries, use $args to query for dynamic data, sort and limit your results, and perform index testing.
For a high-level overview of Ditto create, read, update, and delete (CRUD) operations, see Ditto Basics > CRUD Fundamentals.
Ditto's query language is similar to what you'd write in most if statements. In addition, you can use intuitive query condition operators. For more information, see Ditto Basics > Query Syntax and Platform Manual > Querying Techniques.
If you want to receive detailed information about the types of data being returned, specify the key serializedAs: latestValuesAndTypes in your request.
As demonstrated in the following snippet, you query documents by their collection, rather than by individual document.
However, if you need to find a specific document, you can query by its unique identifier. For more information, see Finding by Document ID.
Instead of building or interpolating query strings, you can query Ditto using runtime variables through an $args map object:
To retrieve a single document by its unique identifier (id) or, if applicable, composite key, use the following endpoint:
If retrieving a document based on a composite key, make sure to provide all of the fields that make up the compound identifier. For more information, see Platform Manual > Identifiers.
For example, the following snippet shows how to construct a cURL request to retrieve a document within the people collection with the document ID of 123abc:
The find method fetches the current version of multiple documents from the Big Peer:
Do not include a find query within a write command in a single operation. Instead, perform each as separate API calls. For instructions, see Performing Find and Write Operations.
Do not include a find query within a write command in a single operation. Instead, perform each operation as separate API calls:
Send a find request to fetch the documents.
Once you've received a response, send a separate write request to create or modify documents.
Unless you explicitly specify a sort direction in your request, the documents are returned in an arbitrary order.
In previous versions of the HTTP API, there was an implicit default sorting order; however, as of HTTP API version 4, documents return in an arbitrary order by default.
If you want to maintain the same default sorting order as previous versions, add sort by _id ascending in your request as follows:
"sort": [ {"property": "_id", "direction": "asc"} ]
The following snippet provides an example of two sort operations:
- Sort documents with name field property set to ascending (asc) order.
- Sort documents with the age field property set to descending (desc) order.
Limit the number of results that a query returns by calling the limit method before executing your query.
For example, the following snippet demonstrates a limit of 100 results for documents within the people collection with a field property of color set to the value of red:
Query efficiency impacts the overall performance and scalability of your app.
To determine how the particular query interacts with an index on the Big Peer, perform an index test by including the describe field set to truein the JSON body of your request.
For example:
If the query successfully made use of an index, you'll receive the following "index_scan" response:
If the query failed to use an index, you'll receive the following "full_scan" response:
Do not include a find query within a write command in a single operation. Instead, perform the following as separate API calls:
Send a find request to fetch the documents.
Once you've received a response, send a separate write request to create create or modify documents.
When you want to ensure whether documents have been successfully synced to the Big peer or evaluate and test the amount of data that a subscription will sync to Small Peers, use the count command:
Accessible using the following URL endpoint, the count command determines the number of documents that match a specific query expression at a particular moment in time:
With the count command, you can write queries directly in your request or, if querying dynamic data, pass them as $args. For more information about using $args, see the Platform Manual > Querying Dynamic Data Using $args.
For example, the following snippet illustrates how to count the number of documents within the people collection with the field property of name set to the value of John: