View Source Dynamo.Update (Dynamo v0.2.0)

Builds DynamoDB UpdateExpressions from a keyword list or map of changes.

Used by Dynamo.Repo.update/3 and Dynamo.Repo.transaction/2. Values are dumped with the schema's field type when a schema is given, otherwise with :any.

Dynamo.Update.build(User, name: "Jane", login_count: {:increment, 1}, legacy: :remove)
#=> {:ok, %{
#     "UpdateExpression" => "SET #a0 = :v0, #a1 = #a1 + :v1 REMOVE #a2",
#     "ExpressionAttributeNames" => %{"#a0" => "name", "#a1" => "login_count", "#a2" => "legacy"},
#     "ExpressionAttributeValues" => %{":v0" => %{"S" => "Jane"}, ":v1" => %{"N" => "1"}}
#   }}

Operators

  • value – SET field = value
  • {:increment, n} / {:decrement, n} – SET field = field + n (field must exist)
  • {:add, n} – ADD field n (atomic counter; creates the attribute if missing)
  • {:add, set} – ADD field set (adds elements to a set)
  • {:delete, set} – DELETE field set (removes elements from a set)
  • {:append, list} / {:prepend, list} – SET field = list_append(...)
  • {:if_not_exists, value} – SET field = if_not_exists(field, value)
  • :remove – REMOVE field

Placeholders are generated (#a0, :v0…) so attribute names never need to be valid identifiers and reserved words are always safe.

Summary

Types

change()
result()

Functions

build(schema, changes)

Builds the expression parts. schema may be nil (values dumped as :any). Key fields of the schema are rejected — updating a key requires delete + put.

Types

change()

@type change() ::
  term()
  | {:increment, number()}
  | {:decrement, number()}
  | {:add, number() | MapSet.t()}
  | {:delete, MapSet.t()}
  | {:append, list()}
  | {:prepend, list()}
  | {:if_not_exists, term()}
  | :remove

result()

@type result() :: %{required(String.t()) => String.t() | map()}

Functions

build(schema, changes)

@spec build(module() | nil, keyword() | map()) ::
  {:ok, result()} | {:error, Dynamo.Error.t()}

Builds the expression parts. schema may be nil (values dumped as :any). Key fields of the schema are rejected — updating a key requires delete + put.