Query.md

Dynamoose provides the ability to query a model by using the Model.query function. This function acts as a builder to construct your query with the appropriate settings before executing it (query.exec).

Model.query([filter])

This is the basic entry point to construct a query request. When running a query you must specify at least the hashKey of the document(s). This can either be the hashKey of the table, or the hashKey of an index. The filter property is optional and can either be an object or a string representing the key you which to first filter on. In the event you don't pass in any parameters and don't call any other methods on the query object it will query with no filters or options.

Cat.query("breed").contains("Terrier").exec() // will query all documents where the hashKey `breed` contains `Terrier`
Cat.query({"breed": {"contains": "Terrier"}}).exec() // will query all documents where the hashKey `breed` contains `Terrier`

If you pass an object into Model.query the object for each key should contain the comparison type. For example, in the last example above, contains was our comparison type. This comparison type must match one of the comparison type functions listed on this page.

Model.query() combines both the KeyConditionExpression and the FilterExpression from DynamoDB. If you query for an attribute that you defined as your hashKey or rangeKey DynamoDB will use KeyConditionExpression. This could be the most performant and cost efficient way to query for. If querying for attributes that are not defined as your hashKey or rangeKey DynamoDB might select more documents at first and then filter the result which could have a bad impact on performance and costs.

Conditionals

On top of all of the methods listed below, every Query instance has all of the methods that a Condition instance has. This means you can use methods like where, filter, eq, lt and more.

Please check the Condition documentation to find the rest of the methods you can use with Query.

query.exec([callback])

This will execute the query you constructed. If you pass in a callback the callback function will be executed upon completion passing in an error (if exists), and the results array. In the event you didn't pass in a callback parameter, a promise will be returned that will resolve to the results array upon completion.

Cat.query("name").eq("Will").exec((error, results) => {
	if (error) {
		console.error(error);
	} else {
		console.log(results);
		// [ Document { name: 'Will', breed: 'Terrier', id: 1 },
		//   lastKey: undefined,
		//   count: 1,
		//   queriedCount: 2,
		//   timesQueried: 1 ]
		console.log(results[0]); // { name: 'Will', breed: 'Terrier', id: 1 }
		console.log(results.count); // 1
		console.log(Array.isArray(results)); // true
		console.log(results.scannedCount); // 2
	}
});

const results = await Cat.query().exec();
// `results` is identical to what is listed in the callback version of this function.

The results array you receive back is a standard JavaScript array of objects. However, the array has some special properties with extra information about your query operation that you can access. This does not prevent the ability do running loops or accessing the objects within the array.

The extra properties attached to the array are:

Name	Description
lastKey	In the event there are more documents to query in DynamoDB this property will be equal to an object that you can pass into query.startAt(key) to retrieve more documents. Normally DynamoDB returns this property as a DynamoDB object, but Dynamoose returns it and handles it as a standard JS object without the DynamoDB types.
count	The count property from DynamoDB, which represents how many documents were returned from DynamoDB. This should always equal the number of documents in the array.
queriedCount	How many documents DynamoDB queried. This doesn't necessarily represent how many documents were returned from DynamoDB due to filters that might have been applied to the query request.
timesQueried	How many times Dynamoose made a query request to DynamoDB. This will always equal 1, unless you used the query.all or query.parallel method.

query.limit(count)

This function will limit the number of documents that DynamoDB will query in this request. Unlike most SQL databases this does not guarantee the response will contain 5 documents. Instead DynamoDB will only query a maximum of 5 documents to see if they match and should be returned. The count parameter passed in should be a number representing how many documents you wish DynamoDB to query.

Cat.query("name").eq("Will").limit(5); // Limit query request to 5 documents

query.startAt(key)

In the event there are more documents to query in a previous response, Dynamoose will return a key in the .lastKey property. You can pass that object into this property to further query documents in your table.

Although the .lastKey property returns a standard (non DynamoDB) object, you can pass a standard object OR DynamoDB object into this function, and it will handle either case.

const response = await Cat.query("name").eq("Will").exec();
const moreDocuments = Cat.query("name").eq("Will").startAt(response.lastKey);

query.attributes(attributes)

This function will limit which attributes DynamoDB returns for each item in the table. This can limit the size of the DynamoDB response and helps you only retrieve the data you need. The attributes property passed into this function should be an array of strings representing the property names you wish DynamoDB to return.

Cat.query("name").eq("Will").attributes(["id", "name"]); // Return all documents but only return the `id` & `name` properties for each item

This function uses the ProjectionExpression DynamoDB property to save bandwidth and not send the entire item over the wire.

query.count()

Instead of returning an array of documents this function will cause the query operation to return a special object with the count information for the query. The response you will receive from the query operation with this setting will be an object with the properties count & queriedCount, which have the same values as described in query.exec([callback]).

Using this option will save bandwidth by setting the DynamoDB Select option to COUNT.

const response = await Cat.query("name").eq("Will").count().exec();
console.log(response); // {"count": 1, "queriedCount": 1}

query.consistent()

This will cause the query to run in a consistent manner as opposed to the default eventually consistent manner.

Cat.query("name").eq("Will").consistent(); // Run the query in a consistent manner

query.using(index)

This causes the query to be run on a specific index as opposed to the default table wide query. The index parameter you pass in should represent the name of the index you wish to query on.

Cat.query("name").eq("Will").using("name-index"); // Run the query on the `name-index` index

query.all([delay[, max]])

Unlike most other query functions that directly change the DynamoDB query request, this function is purely internal and unique to Dynamoose. If a query result is more than the AWS query response limit, DynamoDB paginates the results so you would have to send multiple requests. This function sends continuous query requests upon receiving the response until all documents have been received (by checking and making new requests with the lastKey property from the previous response). This can be useful if you wish to get all the documents from the table and don't want to worry about checking the lastKey property and sending a new query request yourself.

Two parameters can be specified on this setting:

• delay - Number (default: 0) - The number of milliseconds to delay between receiving of the response of one query request and sending of the request for the next query request.
• max - Number (default: 0) - The maximum number of requests that should be made to DynamoDB, regardless of if the lastKey property still exists in the response. In the event this is set to 0, an unlimited number of requests will be made to DynamoDB, so long as the lastKey property still exists.

The documents for all of the requests will be merged into a single array with the count & queriedCount properties being summed in the response. If you set a maximum number of query requests and there is still a lastKey on the response that will be returned to you.

Cat.query("name").eq("Will").all(); // Query table and so long as the `lastKey` property exists continuously query the table to retrieve all documents
Cat.query("name").eq("Will").all(100); // Query table and so long as the `lastKey` property exists continuously query the table to retrieve all documents with a 100 ms delay before the next query request
Cat.query("name").eq("Will").all(0, 5); // Query table and so long as the `lastKey` property exists continuously query the table to retrieve all documents with a maximum of 5 requests total