DynamoDB Dynomite Querying Find

Find Uses get_tiem

You provide the unique id to the find method. Example:

Product.find("product-Q1xnDhRzIYduWAtU")

Underneath the hood, find uses then the get_item to fetch the data using the Primary Key fields, usually id.

Related: model id

Hash Notation and Options

You can also use a Hash to provide the Primary Key:

Post.find("post-TiphkbRQS2pfwMBB")     # partition_key id is discovered
Post.find(id: "post-TiphkbRQS2pfwMBB") # partition_key is specified as id

You can provide additional get_item options as the last Hash argument.

Post.find("post-TiphkbRQS2pfwMBB", consistent_read: true) # partition_key is discovered
Post.find({id: "post-TiphkbRQS2pfwMBB"}, consistent_read: true) # partition_key is specified as id

Composite Key

When the table has a Partition Key and Sort Key, you must specify both as they make up the full Primary Key. For example, given a Product model with a partition_key: category and sort_key: sku. You can find a Product like so:

Product.find(category: "Electronics", sku: 101)

You can provide additional get_item options as the last Hash argument.

Product.find({category: "Electronics", sku: 101}, consistent_read: true)

If you do not provide both partition_key and sort_key values, you’ll get an error:

> Product.find("Electronics")
.../gems/aws-sdk-core-3.180.0/lib/seahorse/client/plugins/raise_response_errors.rb:17:in `call': The provided key element does not match the schema (Aws::DynamoDB::Errors::ValidationException)

Find Multiple Results

Usually, find returns a single item. However, you can also use find and return multiple results. You can pass an Array or splat arguments in different forms.

id1, id2 = Post.first.id, Post.last.id
Post.find(id1, id2)
Post.find([id1, id2])
Post.find([{id: id1}, {id: id2}])
# Composite Keys
Product.find([{category: "Electronics", sku: 101}, {category: "Electronics", sku: 102}])

Underneath the hood, dynomite calls fast get_item in parallel threads in batches of 100. This can be configured with an env var DYNOMITE_GET_ITEMS_THREADS=100.

find cheatsheat

Here are different ways to use find. Post has a partition key only, and Product has a composite key (both partition key and sort key).

Post.find("post-TiphkbRQS2pfwMBB")
Post.find(id: "post-TiphkbRQS2pfwMBB")
Post.find("post-TiphkbRQS2pfwMBB", consistent_read: true)
Post.find({id: "post-TiphkbRQS2pfwMBB"}, consistent_read: true)
Product.find(category: "Electronics", sku: 101)
Product.find({category: "Electronics", sku: 101}, consistent_read: true)

find vs find_by

The find and find_by interfaces are different.

  • find will raise a Dynomite::Error::RecordNotFound if the item is not found. find_by will return nil.
  • find can be passed a single element, Hash, or multiple elements with the Primary Keys. Underneath the hood find only uses get_item for fast lookup.
  • find_by can be passed an Hash. It can use either get_item or where, which can call a query or scan

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