defmodule Ecto.Query.API do
@moduledoc """
Lists all functions allowed in the query API.
* Comparison operators: `==`, `!=`, `<=`, `>=`, `<`, `>`
* Arithmetic operators: `+`, `-`, `*`, `/`
* Boolean operators: `and`, `or`, `not`
* Inclusion operator: `in/2`
* Subquery operators: `any`, `all` and `exists`
* Search functions: `like/2` and `ilike/2`
* Null check functions: `is_nil/1`
* Aggregates: `count/0`, `count/1`, `avg/1`, `sum/1`, `min/1`, `max/1`
* Date/time intervals: `datetime_add/3`, `date_add/3`, `from_now/2`, `ago/2`
* Inside select: `struct/2`, `map/2`, `merge/2`, `selected_as/2` and literals (map, tuples, lists, etc)
* General: `fragment/1`, `field/2`, `type/2`, `as/1`, `parent_as/1`, `selected_as/1`
Note the functions in this module exist for documentation
purposes and one should never need to invoke them directly.
Furthermore, it is possible to define your own macros and
use them in Ecto queries (see docs for `fragment/1`).
## Intervals
Ecto supports following values for `interval` option: `"year"`, `"month"`,
`"week"`, `"day"`, `"hour"`, `"minute"`, `"second"`, `"millisecond"`, and
`"microsecond"`.
`Date`/`Time` functions like `datetime_add/3`, `date_add/3`, `from_now/2`,
`ago/2` take `interval` as an argument.
## Window API
Ecto also supports many of the windows functions found
in SQL databases. See `Ecto.Query.WindowAPI` for more
information.
## About the arithmetic operators
The Ecto implementation of these operators provide only
a thin layer above the adapters. So if your adapter allows you
to use them in a certain way (like adding a date and an
interval in PostgreSQL), it should work just fine in Ecto
queries.
"""
@dialyzer :no_return
@doc """
Binary `==` operation.
"""
def left == right, do: doc!([left, right])
@doc """
Binary `!=` operation.
"""
def left != right, do: doc!([left, right])
@doc """
Binary `<=` operation.
"""
def left <= right, do: doc!([left, right])
@doc """
Binary `>=` operation.
"""
def left >= right, do: doc!([left, right])
@doc """
Binary `<` operation.
"""
def left < right, do: doc!([left, right])
@doc """
Binary `>` operation.
"""
def left > right, do: doc!([left, right])
@doc """
Binary `+` operation.
"""
def left + right, do: doc!([left, right])
@doc """
Binary `-` operation.
"""
def left - right, do: doc!([left, right])
@doc """
Binary `*` operation.
"""
def left * right, do: doc!([left, right])
@doc """
Binary `/` operation.
"""
def left / right, do: doc!([left, right])
@doc """
Binary `and` operation.
"""
def left and right, do: doc!([left, right])
@doc """
Binary `or` operation.
"""
def left or right, do: doc!([left, right])
@doc """
Unary `not` operation.
It is used to negate values in `:where`. It is also used to match
the assert the opposite of `in/2`, `is_nil/1`, and `exists/1`.
For example:
from p in Post, where: p.id not in [1, 2, 3]
from p in Post, where: not is_nil(p.title)
# Retrieve all the posts that doesn't have comments.
from p in Post,
as: :post,
where:
not exists(
from(
c in Comment,
where: parent_as(:post).id == c.post_id
)
)
"""
def not value, do: doc!([value])
@doc """
Checks if the left-value is included in the right one.
from p in Post, where: p.id in [1, 2, 3]
The right side may either be a literal list, an interpolated list,
any struct that implements the `Enumerable` protocol, or even a
column in the database with array type:
from p in Post, where: "elixir" in p.tags
Additionally, the right side may also be a subquery, which should return
a single column:
from c in Comment, where: c.post_id in subquery(
from(p in Post, where: p.created_at > ^since, select: p.id)
)
"""
def left in right, do: doc!([left, right])
@doc """
Evaluates to true if the provided subquery returns 1 or more rows.
from p in Post,
as: :post,
where:
exists(
from(
c in Comment,
where: parent_as(:post).id == c.post_id and c.replies_count > 5,
select: 1
)
)
This is best used in conjunction with `parent_as` to correlate the subquery
with the parent query to test some condition on related rows in a different table.
In the above example the query returns posts which have at least one comment that
has more than 5 replies.
"""
def exists(subquery), do: doc!([subquery])
@doc """
Tests whether one or more values returned from the provided subquery match in a comparison operation.
from p in Product, where: p.id == any(
from(li in LineItem, select: [li.product_id], where: li.created_at > ^since and li.qty >= 10)
)
A product matches in the above example if a line item was created since the provided date where the customer purchased
at least 10 units.
Both `any` and `all` must be given a subquery as an argument, and they must be used on the right hand side of a comparison.
Both can be used with every comparison operator: `==`, `!=`, `>`, `>=`, `<`, `<=`.
"""
def any(subquery), do: doc!([subquery])
@doc """
Evaluates whether all values returned from the provided subquery match in a comparison operation.
from p in Post, where: p.visits >= all(
from(p in Post, select: avg(p.visits), group_by: [p.category_id])
)
For a post to match in the above example it must be visited at least as much as the average post in all categories.
from p in Post, where: p.visits == all(
from(p in Post, select: max(p.visits))
)
The above example matches all the posts which are tied for being the most visited.
Both `any` and `all` must be given a subquery as an argument, and they must be used on the right hand side of a comparison.
Both can be used with every comparison operator: `==`, `!=`, `>`, `>=`, `<`, `<=`.
"""
def all(subquery), do: doc!([subquery])
@doc """
Searches for `search` in `string`.
from p in Post, where: like(p.body, "Chapter%")
Translates to the underlying SQL LIKE query, therefore
its behaviour is dependent on the database. In particular,
PostgreSQL will do a case-sensitive operation, while the
majority of other databases will be case-insensitive. For
performing a case-insensitive `like` in PostgreSQL, see `ilike/2`.
You should be very careful when allowing user sent data to be used
as part of LIKE query, since they allow to perform
[LIKE-injections](https://githubengineering.com/like-injection/).
"""
def like(string, search), do: doc!([string, search])
@doc """
Searches for `search` in `string` in a case insensitive fashion.
from p in Post, where: ilike(p.body, "Chapter%")
Translates to the underlying SQL ILIKE query. This operation is
only available on PostgreSQL.
"""
def ilike(string, search), do: doc!([string, search])
@doc """
Checks if the given value is nil.
from p in Post, where: is_nil(p.published_at)
To check if a given value is not nil use:
from p in Post, where: not is_nil(p.published_at)
"""
def is_nil(value), do: doc!([value])
@doc """
Counts the entries in the table.
from p in Post, select: count()
"""
def count, do: doc!([])
@doc """
Counts the given entry.
from p in Post, select: count(p.id)
"""
def count(value), do: doc!([value])
@doc """
Counts the distinct values in given entry.
from p in Post, select: count(p.id, :distinct)
"""
def count(value, :distinct), do: doc!([value, :distinct])
@doc """
Takes the first value which is not null, or null if they both are.
In SQL, COALESCE takes any number of arguments, but in ecto
it only takes two, so it must be chained to achieve the same
effect.
from p in Payment, select: p.value |> coalesce(p.backup_value) |> coalesce(0)
"""
def coalesce(value, expr), do: doc!([value, expr])
@doc """
Applies the given expression as a FILTER clause against an
aggregate. This is currently only supported by Postgres.
from p in Payment, select: filter(avg(p.value), p.value > 0 and p.value < 100)
from p in Payment, select: avg(p.value) |> filter(p.value < 0)
"""
def filter(value, filter), do: doc!([value, filter])
@doc """
Calculates the average for the given entry.
from p in Payment, select: avg(p.value)
"""
def avg(value), do: doc!([value])
@doc """
Calculates the sum for the given entry.
from p in Payment, select: sum(p.value)
"""
def sum(value), do: doc!([value])
@doc """
Calculates the minimum for the given entry.
from p in Payment, select: min(p.value)
"""
def min(value), do: doc!([value])
@doc """
Calculates the maximum for the given entry.
from p in Payment, select: max(p.value)
"""
def max(value), do: doc!([value])
@doc """
Adds a given interval to a datetime.
The first argument is a `datetime`, the second one is the count
for the interval, which may be either positive or negative and
the interval value:
# Get all items published since the last month
from p in Post, where: p.published_at >
datetime_add(^NaiveDateTime.utc_now(), -1, "month")
In the example above, we used `datetime_add/3` to subtract one month
from the current datetime and compared it with the `p.published_at`.
If you want to perform operations on date, `date_add/3` could be used.
See [Intervals](#module-intervals) for supported `interval` values.
"""
def datetime_add(datetime, count, interval), do: doc!([datetime, count, interval])
@doc """
Adds a given interval to a date.
See `datetime_add/3` for more information.
See [Intervals](#module-intervals) for supported `interval` values.
"""
def date_add(date, count, interval), do: doc!([date, count, interval])
@doc """
Adds the given interval to the current time in UTC.
The current time in UTC is retrieved from Elixir and
not from the database.
See [Intervals](#module-intervals) for supported `interval` values.
## Examples
from a in Account, where: a.expires_at < from_now(3, "month")
"""
def from_now(count, interval), do: doc!([count, interval])
@doc """
Subtracts the given interval from the current time in UTC.
The current time in UTC is retrieved from Elixir and
not from the database.
See [Intervals](#module-intervals) for supported `interval` values.
## Examples
from p in Post, where: p.published_at > ago(3, "month")
"""
def ago(count, interval), do: doc!([count, interval])
@doc """
Send fragments directly to the database.
It is not possible to represent all possible database queries using
Ecto's query syntax. When such is required, it is possible to use
fragments to send any expression to the database:
def unpublished_by_title(title) do
from p in Post,
where: is_nil(p.published_at) and
fragment("lower(?)", p.title) == ^title
end
Every occurrence of the `?` character will be interpreted as a place
for parameters, which must be given as additional arguments to
`fragment`. If the literal character `?` is required as part of the
fragment, it can be escaped with `\\\\?` (one escape for strings,
another for fragment).
In the example above, we are using the lower procedure in the
database to downcase the title column.
It is very important to keep in mind that Ecto is unable to do any
type casting when fragments are used. Therefore it may be necessary
to explicitly cast parameters via `type/2`:
fragment("lower(?)", p.title) == type(^title, :string)
## Literals
Sometimes you need to interpolate a literal value into a fragment,
instead of a parameter. For example, you may need to pass a table
name or a collation, such as:
collation = "es_ES"
fragment("? COLLATE ?", ^name, ^collation)
The example above won't work because `collation` will be passed
as a parameter, while it has to be a literal part of the query.
You can address this by telling Ecto that variable is a literal:
fragment("? COLLATE ?", ^name, literal(^collation))
Ecto will then escape it and make it part of the query.
> #### Literals and query caching {: .warning}
>
> Because literals are made part of the query, each interpolated
> literal will generate a separate query, with its own cache.
## Splicing
Sometimes you may need to interpolate a variable number of arguments
into the same fragment. For example, when overriding Ecto's default
`where` behaviour for Postgres:
from p in Post, where: fragment("? in (?, ?)", p.id, val1, val2)
The example above will only work if you know the number of arguments
upfront. If it can vary, the above will not work.
You can address this by telling Ecto to splice a list argument into
the fragment:
from p in Post, where: fragment("? in (?)", p.id, splice(^val_list))
This will let Ecto know it should expand the values of the list into
separate fragment arguments. For example:
from p in Post, where: fragment("? in (?)", p.id, splice(^[1, 2, 3]))
would be expanded into
from p in Post, where: fragment("? in (?,?,?)", p.id, ^1, ^2, ^3)
## Defining custom functions using macros and fragment
You can add a custom Ecto query function using macros. For example
to expose SQL's coalesce function you can define this macro:
defmodule CustomFunctions do
defmacro coalesce(left, right) do
quote do
fragment("coalesce(?, ?)", unquote(left), unquote(right))
end
end
end
To have coalesce/2 available, just import the module that defines it.
import CustomFunctions
The only downside is that it will show up as a fragment when
inspecting the Elixir query. Other than that, it should be
equivalent to a built-in Ecto query function.
## Keyword fragments
In order to support databases that do not have string-based
queries, like MongoDB, fragments also allow keywords to be given:
from p in Post,
where: fragment(title: ["$eq": ^some_value])
"""
def fragment(fragments), do: doc!([fragments])
@doc """
Allows a literal identifier to be injected into a fragment:
collation = "es_ES"
fragment("? COLLATE ?", ^name, literal(^collation))
The example above will inject `collation` into the query as
a literal identifier instead of a query parameter. Note that
each different value of `collation` will emit a different query,
which will be independently prepared and cached.
"""
def literal(binary), do: doc!([binary])
@doc """
Allows a list argument to be spliced into a fragment.
from p in Post, where: fragment("? in (?)", p.id, splice(^[1, 2, 3]))
The example above will be transformed at runtime into the following:
from p in Post, where: fragment("? in (?,?,?)", p.id, ^1, ^2, ^3)
You may only splice runtime values. For example, this would not work because
query bindings are compile-time constructs:
from p in Post, where: fragment("concat(?)", splice(^[p.count, " ", "count"])
"""
def splice(list), do: doc!([list])
@doc """
Creates a values list/constant table.
A values list can be used as a source in a query, both in `Ecto.Query.from/2`
and `Ecto.Query.join/5`.
The first argument is a list of maps representing the values of the constant table.
Each entry in the list must have exactly the same fields or an error is raised.
The second argument is a map of types corresponding to the fields in the first argument.
Each field must be given a type or an error is raised. Any type that can be specified in
a schema may be used.
Queries using a values list are not cacheable by Ecto.
## Select example
values = [%{id: 1, text: "abc"}, %{id: 2, text: "xyz"}]
types = %{id: :integer, text: :string}
query =
from v1 in values(values, types),
join: v2 in values(values, types),
on: v1.id == v2.id
Repo.all(query)
## Delete example
values = [%{id: 1, text: "abc"}, %{id: 2, text: "xyz"}]
types = %{id: :integer, text: :string}
query =
from p in Post,
join: v in values(values, types),
on: p.id == v.id,
where: p.counter == ^0
Repo.delete_all(query)
## Update example
values = [%{id: 1, text: "abc"}, %{id: 2, text: "xyz"}]
types = %{id: :integer, text: :string}
query =
from p in Post,
join: v in values(values, types),
on: p.id == v.id,
update: [set: [text: v.text]]
Repo.update_all(query, [])
"""
def values(values, types), do: doc!([values, types])
@doc """
Allows a field to be dynamically accessed.
def at_least_four(doors_or_tires) do
from c in Car,
where: field(c, ^doors_or_tires) >= 4
end
In the example above, both `at_least_four(:doors)` and `at_least_four(:tires)`
would be valid calls as the field is dynamically generated.
"""
def field(source, field), do: doc!([source, field])
@doc """
Used in `select` to specify which struct fields should be returned.
For example, if you don't need all fields to be returned
as part of a struct, you can filter it to include only certain
fields by using `struct/2`:
from p in Post,
select: struct(p, [:title, :body])
`struct/2` can also be used to dynamically select fields:
fields = [:title, :body]
from p in Post, select: struct(p, ^fields)
As a convenience, `select` allows developers to take fields
without an explicit call to `struct/2`:
from p in Post, select: [:title, :body]
Or even dynamically:
fields = [:title, :body]
from p in Post, select: ^fields
For preloads, the selected fields may be specified from the parent:
from(city in City, preload: :country,
select: struct(city, [:country_id, :name, country: [:id, :population]]))
If the same source is selected multiple times with a `struct`,
the fields are merged in order to avoid fetching multiple copies
from the database. In other words, the expression below:
from(city in City, preload: :country,
select: {struct(city, [:country_id]), struct(city, [:name])})
is expanded to:
from(city in City, preload: :country,
select: {struct(city, [:country_id, :name]), struct(city, [:country_id, :name])})
**IMPORTANT**: When filtering fields for associations, you
MUST include the foreign keys used in the relationship,
otherwise Ecto will be unable to find associated records.
"""
def struct(source, fields), do: doc!([source, fields])
@doc """
Used in `select` to specify which fields should be returned as a map.
For example, if you don't need all fields to be returned or
neither need a struct, you can use `map/2` to achieve both:
from p in Post,
select: map(p, [:title, :body])
`map/2` can also be used to dynamically select fields:
fields = [:title, :body]
from p in Post, select: map(p, ^fields)
If the same source is selected multiple times with a `map`,
the fields are merged in order to avoid fetching multiple copies
from the database. In other words, the expression below:
from(city in City, preload: :country,
select: {map(city, [:country_id]), map(city, [:name])})
is expanded to:
from(city in City, preload: :country,
select: {map(city, [:country_id, :name]), map(city, [:country_id, :name])})
For preloads, the selected fields may be specified from the parent:
from(city in City, preload: :country,
select: map(city, [:country_id, :name, country: [:id, :population]]))
It's also possible to select a struct from one source but only a subset of
fields from one of its associations:
from(city in City, preload: :country,
select: %{city | country: map(country: [:id, :population])})
**IMPORTANT**: When filtering fields for associations, you
MUST include the foreign keys used in the relationship,
otherwise Ecto will be unable to find associated records.
"""
def map(source, fields), do: doc!([source, fields])
@doc """
Merges the map on the right over the map on the left.
If the map on the left side is a struct, Ecto will check
all of the field on the right previously exist on the left
before merging.
from(city in City, select: merge(city, %{virtual_field: "some_value"}))
This function is primarily used by `Ecto.Query.select_merge/3`
to merge different select clauses.
"""
def merge(left_map, right_map), do: doc!([left_map, right_map])
@doc """
Returns value from the `json_field` pointed to by `path`.
from(post in Post, select: json_extract_path(post.meta, ["author", "name"]))
The path can be dynamic:
path = ["author", "name"]
from(post in Post, select: json_extract_path(post.meta, ^path))
And the field can also be dynamic in combination with it:
path = ["author", "name"]
from(post in Post, select: json_extract_path(field(post, :meta), ^path))
The query can be also rewritten as:
from(post in Post, select: post.meta["author"]["name"])
Path elements can be integers to access values in JSON arrays:
from(post in Post, select: post.meta["tags"][0]["name"])
Any element of the path can be dynamic:
field = "name"
from(post in Post, select: post.meta["author"][^field])
## Warning: indexes on PostgreSQL
PostgreSQL supports indexing on jsonb columns via GIN indexes.
Whenever comparing the value of a jsonb field against a string
or integer, Ecto will use the containment operator @> which
is optimized. You can even use the more efficient `jsonb_path_ops`
GIN index variant. For more information, consult PostgreSQL's docs
on [JSON indexing](https://www.postgresql.org/docs/current/datatype-json.html#JSON-INDEXING).
## Warning: return types
The underlying data in the JSON column is returned without any
additional decoding. This means "null" JSON values are not the
same as SQL's "null". For example, the `Repo.all` operation below
returns an empty list because `p.meta["author"]` returns JSON's
null and therefore `is_nil` does not succeed:
Repo.insert!(%Post{meta: %{author: nil}})
Repo.all(from(post in Post, where: is_nil(p.meta["author"])))
Similarly, other types, such as datetimes, are returned as strings.
This means conditions like `post.meta["published_at"] > from_now(-1, "day")`
may return incorrect results or fail as the underlying database
tries to compare incompatible types. You can, however, use `type/2`
to force the types on the database level.
"""
def json_extract_path(json_field, path), do: doc!([json_field, path])
@doc """
Casts the given value to the given type at the database level.
Most of the times, Ecto is able to proper cast interpolated
values due to its type checking mechanism. In some situations
though, you may want to tell Ecto that a parameter has some
particular type:
type(^title, :string)
It is also possible to say the type must match the same of a column:
type(^title, p.title)
Or a parameterized type, which must be previously initialized
with `Ecto.ParameterizedType.init/2`:
@my_enum Ecto.ParameterizedType.init(Ecto.Enum, values: [:foo, :bar, :baz])
type(^title, ^@my_enum)
Ecto will ensure `^title` is cast to the given type and enforce such
type at the database level. If the value is returned in a `select`,
Ecto will also enforce the proper type throughout.
When performing arithmetic operations, `type/2` can be used to cast
all the parameters in the operation to the same type:
from p in Post,
select: type(p.visits + ^a_float + ^a_integer, :decimal)
Inside `select`, `type/2` can also be used to cast fragments:
type(fragment("NOW"), :naive_datetime)
Or to type fields from schemaless queries:
from p in "posts", select: type(p.cost, :decimal)
Or to type aggregation results:
from p in Post, select: type(avg(p.cost), :integer)
from p in Post, select: type(filter(avg(p.cost), p.cost > 0), :integer)
Or to type comparison expression results:
from p in Post, select: type(coalesce(p.cost, 0), :integer)
Or to type fields from a parent query using `parent_as/1`:
child = from c in Comment, where: type(parent_as(:posts).id, :string) == c.text
from Post, as: :posts, inner_lateral_join: c in subquery(child), select: c.text
## `type` vs `fragment`
`type/2` is all about Ecto types. Therefore, you can perform `type(expr, :string)`
but not `type(expr, :text)`, because `:text` is not an actual Ecto type. If you want
to perform casting exclusively at the database level, you can use fragment. For example,
in PostgreSQL, you might do `fragment("?::text", p.column)`.
"""
def type(interpolated_value, type), do: doc!([interpolated_value, type])
@doc """
Refer to a named atom binding.
See the "Named bindings" section in `Ecto.Query` for more information.
"""
def as(binding), do: doc!([binding])
@doc """
Refer to a named atom binding in the parent query.
This is available only inside subqueries.
See the "Named bindings" section in `Ecto.Query` for more information.
"""
def parent_as(binding), do: doc!([binding])
@doc """
Refer to an alias of a selected value.
This can be used to refer to aliases created using `selected_as/2`. If
the alias hasn't been created using `selected_as/2`, an error will be raised.
Each database has its own rules governing which clauses can reference these aliases.
If an error is raised mentioning an unknown column, most likely the alias is being
referenced somewhere that is not allowed. Consult the documentation for the database
to ensure the alias is being referenced correctly.
"""
def selected_as(name), do: doc!([name])
@doc """
Creates an alias for the given selected value.
When working with calculated values, an alias can be used to simplify
the query. Otherwise, the entire expression would need to be copied when
referencing it outside of select statements.
This comes in handy when, for instance, you would like to use the calculated
value in `Ecto.Query.group_by/3` or `Ecto.Query.order_by/3`:
from p in Post,
select: %{
posted: selected_as(p.posted, :date),
sum_visits: p.visits |> coalesce(0) |> sum() |> selected_as(:sum_visits)
},
group_by: selected_as(:date),
order_by: selected_as(:sum_visits)
The name of the alias must be an atom and it can only be used in the outer most
select expression, otherwise an error is raised. Please note that the alias name
does not have to match the key when `select` returns a map, struct or keyword list.
Using this in conjunction with `selected_as/1` is recommended to ensure only defined aliases
are referenced.
## Subqueries and CTEs
Subqueries and CTEs automatically alias the selected fields, for example, one can write:
# Subquery
s = from p in Post, select: %{visits: coalesce(p.visits, 0)}
from(s in subquery(s), select: s.visits)
# CTE
cte_query = from p in Post, select: %{visits: coalesce(p.visits, 0)}
Post |> with_cte("cte", as: ^cte_query) |> join(:inner, [p], c in "cte") |> select([p, c], c.visits)
However, one can also use `selected_as` to override the default naming:
# Subquery
s = from p in Post, select: %{visits: coalesce(p.visits, 0) |> selected_as(:num_visits)}
from(s in subquery(s), select: s.num_visits)
# CTE
cte_query = from p in Post, select: %{visits: coalesce(p.visits, 0) |> selected_as(:num_visits)}
Post |> with_cte("cte", as: ^cte_query) |> join(:inner, [p], c in "cte") |> select([p, c], c.num_visits)
The name given to `selected_as/2` can also be referenced in `selected_as/1`,
as in regular queries.
"""
def selected_as(selected_value, name), do: doc!([selected_value, name])
defp doc!(_) do
raise "the functions in Ecto.Query.API should not be invoked directly, " <>
"they serve for documentation purposes only"
end
end
