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Ecto.Query.API

This module lists all functions allowed in the query API.

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).

Summary

Functions

left != right

Binary != operation

left < right

Binary < operation

left <= right

Binary <= operation

left == right

Binary == operation

left > right

Binary > operation

left >= right

Binary >= operation

ago(count, interval)

Substracts the given interval from the current time in UTC

left and right

Binary and operation

avg(value)

Calculates the average for the given entry

count(value)

Counts the given entry

count(value, atom)

Counts the distinct values in given entry

date_add(date, count, interval)

Adds a given interval to a date

datetime_add(datetime, count, interval)

Adds a given interval to a datetime

field(source, field)

Allows a field to be dynamically accessed

fragment(fragments)

Send fragments directly to the database

from_now(count, interval)

Adds the given interval to the current time in UTC

ilike(string, search)

Searches for search in string in a case insensitive fashion

left in right

Checks if the left-value is included in the right one

is_nil(value)

Checks if the given value is nil

like(string, search)

Searches for search in string

map(source, fields)

Used in select to specify which fields should be returned as a map

max(value)

Calculates the maximum for the given entry

min(value)

Calculates the minimum for the given entry

not value

Unary not operation

left or right

Binary or operation

struct(source, fields)

Used in select to specify which struct fields should be returned

sum(value)

Calculates the sum for the given entry

type(interpolated_value, type)

Casts the given value to the given type

Functions

left != right

Binary != operation.

left < right

Binary < operation.

left <= right

Binary <= operation.

left == right

Binary == operation.

left > right

Binary > operation.

left >= right

Binary >= operation.

ago(count, interval)

Substracts the given interval from the current time in UTC.

The current time in UTC is retrieved from Elixir and not from the database.

Examples

from p in Post, where: p.published_at > ago(3, "month")

left and right

Binary and operation.

avg(value)

Calculates the average for the given entry.

from p in Payment, select: avg(p.value)

count(value)

Counts the given entry.

from p in Post, select: count(p.id)

count(value, atom)

Counts the distinct values in given entry.

from p in Post, select: count(p.id, :distinct)

date_add(date, count, interval)

Adds a given interval to a date.

See datetime_add/3 for more information.

datetime_add(datetime, count, interval)

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(^Ecto.DateTime.utc, -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.

The following intervals are supported: year, month, week, day, hour, minute, second, millisecond and microsecond.

field(source, field)

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.

fragment(fragments)

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

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 described above when fragments are used. You can however use the type/2 function to give Ecto some hints:

fragment("lower(?)", p.title) == type(^title, :string)

Or even say the right side is of the same type as p.title:

fragment("lower(?)", p.title) == type(^title, p.title)

It is possible to make use of PostgreSQL’s JSON/JSONB data type with fragments, as well:

fragment("?->>? ILIKE ?", p.map, "key_name", ^some_value)

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])

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.

from_now(count, interval)

Adds the given interval to the current time in UTC.

The current time in UTC is retrieved from Elixir and not from the database.

Examples

from a in Account, where: a.expires_at < from_now(3, "month")

ilike(string, search)

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.

left in right

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 list, a literal list or even a column in the database with array type:

from p in Post, where: "elixir" in p.tags

is_nil(value)

Checks if the given value is nil.

from p in Post, where: is_nil(p.published_at)

like(string, search)

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.

map(source, fields)

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)

map/2 is also useful when you want to limit the fields of different structs:

from(city in City, join: country in assoc(city, :country),
     select: {map(city, [:country_id, :name]), map(country, [:id, :population])}

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]]))

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.

max(value)

Calculates the maximum for the given entry.

from p in Payment, select: max(p.value)

min(value)

Calculates the minimum for the given entry.

from p in Payment, select: min(p.value)

not value

Unary not operation.

left or right

Binary or operation.

struct(source, fields)

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

However, struct/2 is still useful when you want to limit the fields of different structs:

from(city in City, join: country in assoc(city, :country),
     select: {struct(city, [:country_id, :name]), struct(country, [:id, :population])}

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]]))

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.

sum(value)

Calculates the sum for the given entry.

from p in Payment, select: sum(p.value)

type(interpolated_value, type)

Casts the given value to the given type.

Most of the times, Ecto is able to proper cast interpolated values due to its type checking mechanism. In some situations though, in particular when using fragments with fragment/1, you may want to tell Ecto you are expecting a particular type:

fragment("lower(?)", p.title) == type(^title, :string)

It is also possible to say the type must match the same of a column:

fragment("lower(?)", p.title) == type(^title, p.title)

© 2012 Plataformatec
Licensed under the Apache License, Version 2.0.
https://hexdocs.pm/ecto/Ecto.Query.API.html