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The representation of a filter in Ash.

Security Concerns

If you are using a map with string keys, it is likely that you are parsing input. It is important to note that, instead of passing a filter supplied from an external source directly to Ash.Query.filter/2, you should call Ash.Filter.parse_input/2. This ensures that the filter only uses public attributes, relationships, aggregates and calculations, honors field policies and any policies on related resources.

Writing a filter

Built In Predicates

  • is_nil
  • ==
  • !=
  • in
  • <
  • >
  • <=
  • >=
  • &&
  • ||
  • <>
  • /
  • -
  • *
  • +
  • equals (alias for ==)
  • not_equals (alias for !=)
  • gt (alias for >)
  • lt (alias for <)
  • gte (alias for >=)
  • lte (alias for <=)
  • eq (alias for ==)
  • not_eq (alias for !=)
  • less_than (alias for <)
  • greater_than (alias for >)
  • less_than_or_equal (alias for <=)
  • greater_than_or_equal (alias for >=)
  • and (alias for &&)
  • or (alias for ||)
  • concat (alias for <>)
  • div (alias for /)
  • minus (alias for -)
  • times (alias for *)
  • plus (alias for +)

BooleanExpression syntax

The expression syntax ultimately just builds the keyword list style filter, but with lots of conveniences that would be very annoying to do manually.

Examples

Ash.Query.filter(resource, name == "Zardoz")
Ash.Query.filter(resource, first_name == "Zar" and last_name == "Doz")
Ash.Query.filter(resource, first_name == "Zar" and last_name in ["Doz", "Daz"] and high_score > 10)
Ash.Query.filter(resource, first_name == "Zar" or last_name == "Doz" or (high_score > 10 and high_score < -10))

Expressions

More complex filters can be built using Ash Expressions.

Examples

# Filter based on the contents of a string attribute
Ash.Query.filter(Helpdesk.Support.Ticket, contains(subject, "2"))
# Filter based on the attribute of a joined relationship:
Ash.Query.filter(Helpdesk.Support.Ticket, representative.name == ^name)

See the Expressions guide guide for more information.

Keyword list syntax

A filter is a nested keyword list (with some exceptions, like true for everything and false for nothing).

The key is the "predicate" (or "condition") and the value is the parameter. You can use and and or to create nested filters. Data layers can expose custom predicates. Eventually, you will be able to define your own custom predicates, which will be a mechanism for you to attach complex filters supported by the data layer to your queries.

Important In a given keyword list, all predicates are considered to be "ands". So [or: [first_name: "Tom", last_name: "Bombadil"]] doesn't mean 'First name == "tom" or last_name == "bombadil"'. To say that, you want to provide a list of filters, like so: [or: [[first_name: "Tom"], [last_name: "Bombadil"]]]

Some example filters:

Ash.Query.filter(resource, [name: "Zardoz"])
Ash.Query.filter(resource, [first_name: "Zar", last_name: "Doz"])
Ash.Query.filter(resource, [first_name: "Zar", last_name: [in: ["Doz", "Daz"]], high_score: [greater_than: 10]])
Ash.Query.filter(resource, [or: [
  [first_name: "Zar"],
  [last_name: "Doz"],
  [or: [
    [high_score: [greater_than: 10]]],
    [high_score: [less_than: -10]]
  ]
]])

Other formats

Maps are also accepted, as are maps with string keys. Technically, a list of [{"string_key", value}] would also work.

Summary

Functions

Find an expression inside of a filter that matches the provided predicate

Can be used to find a simple equality predicate on an attribute

Returns a filter statement that would find a single record based on the input.

Parses a filter statement

Parses a filter statement, accepting only public attributes/relationships, honoring field policies & related resource policies.

Parses a filter statement, accepting only public attributes/relationships, honoring field policies & related resource policies, raising on errors.

Returns true if the second argument is a strict subset (always returns the same or less data) of the first

Transform an expression based filter to a simple filter, which is just a list of predicates

Types

@type t() :: %Ash.Filter{expression: term(), resource: term()}

Functions

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add_to_filter(base, addition, op \\ :and, aggregates \\ %{}, calculations \\ %{}, context \\ %{})

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add_to_filter!(base, addition, op \\ :and, aggregates \\ %{}, calculations \\ %{}, context \\ %{})

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builtin_predicate_operators()

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custom_expression(name, args)

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do_hydrate_refs(ref, context)

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find(expr, pred, ors? \\ true, ands? \\ true)

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Find an expression inside of a filter that matches the provided predicate

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find_simple_equality_predicate(expression, attribute)

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Can be used to find a simple equality predicate on an attribute

Use this when your attribute is configured with filterable? :simple_equality, and you want to to find the value that it is being filtered on with (if any).

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flat_map(expression, func)

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get_filter(resource, id)

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Returns a filter statement that would find a single record based on the input.

For example:

iex> get_filter(MyApp.Post, 1)
{:ok, %{id: 1}} #using primary key
iex> get_filter(MyApp.Post, id: 1)
{:ok, %{id: 1}} #using primary key
iex> get_filter(MyApp.Post, author_id: 1, publication_id: 2, first_name: "fred")
{:ok, %{author_id: 1, publication_id: 1}} # using a unique identity
iex> get_filter(MyApp.Post, first_name: "fred")
:error # not enough information
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get_function(key, resource, public?)

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get_predicate_function(key, resource, public?)

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hydrate_refs(value, context)

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list_predicates(expression)

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list_refs(expression, no_longer_simple? \\ false, in_an_eq? \\ false, expand_calculations? \\ false, expand_get_path? \\ false)

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move_exprs_to_relationship_path(refs, path)

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move_to_relationship_path(expression, relationship_path)

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parse(resource, statement, context \\ %{})

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Parses a filter statement

See the module documentation for more information on the supported formats for filter statements.

Important

If you are trying to validate a filter supplied from an external/untrusted source, be sure to use parse_input/2 instead! The only difference is that it only accepts filters over public attributes/relationships.

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parse!(resource, statement, context \\ %{})

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Parses a filter statement

See parse/2 for more

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parse_input(resource, statement)

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Parses a filter statement, accepting only public attributes/relationships, honoring field policies & related resource policies.

See parse/2 for more

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parse_input!(resource, statement)

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Parses a filter statement, accepting only public attributes/relationships, honoring field policies & related resource policies, raising on errors.

See parse_input/2 for more

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put_at_path(value, list)

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relationship_paths(filter_or_expression, include_exists? \\ false, with_refs? \\ false, expand_aggregates? \\ false)

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run_other_data_layer_filters(domain, resource, filter, tenant)

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strict_subset_of(filter, candidate)

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Returns true if the second argument is a strict subset (always returns the same or less data) of the first

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strict_subset_of?(filter, candidate)

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to_simple_filter(map, opts \\ [])

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Transform an expression based filter to a simple filter, which is just a list of predicates

Options:

  • skip_invalid?:
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update_aggregates(expression, mapper, nested_path \\ [], parent_paths \\ [])

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used_aggregates(filter, relationship_path \\ [], return_refs? \\ false)

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used_calculations(filter, resource, relationship_path \\ [], calculations \\ %{}, aggregates \\ %{}, return_refs? \\ false)

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