Ecto v3.1.6 Ecto.Query.API View Source

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).

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.

Link to this section Summary

Functions

Binary != operation.

Binary * operation.

Binary + operation.

Binary - operation.

Binary / operation.

Binary < operation.

Binary <= operation.

Binary == operation.

Binary > operation.

Binary >= operation.

Subtracts the given interval from the current time in UTC.

Binary and operation.

Calculates the average for the given entry.

Takes whichever value is not null, or null if they both are.

Counts the entries in the table.

Counts the given entry.

Counts the distinct values in given entry.

Adds a given interval to a date.

Adds a given interval to a datetime.

Allows a field to be dynamically accessed.

Applies the given expression as a FILTER clause against an aggregate. This is currently only supported by Postgres.

Send fragments directly to the database.

Adds the given interval to the current time in UTC.

Searches for search in string in a case insensitive fashion.

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

Checks if the given value is nil.

Searches for search in string.

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

Calculates the maximum for the given entry.

Merges the map on the right over the map on the left.

Calculates the minimum for the given entry.

Unary not operation.

Binary or operation.

Used in select to specify which struct fields should be returned.

Calculates the sum for the given entry.

Casts the given value to the given type at the database level.

Link to this section Functions

Binary != operation.

Binary * operation.

Binary + operation.

Binary - operation.

Binary / operation.

Binary < operation.

Binary <= operation.

Binary == operation.

Binary > operation.

Binary >= operation.

Subtracts 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")

Binary and operation.

Calculates the average for the given entry.

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

Takes whichever value 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)

Counts the entries in the table.

from p in Post, select: count()

Counts the given entry.

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

Counts the distinct values in given entry.

from p in Post, select: count(p.id, :distinct)
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date_add(date, count, interval) View Source

Adds a given interval to a date.

See datetime_add/3 for more information.

Link to this function

datetime_add(datetime, count, interval) View Source

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.

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

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.

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)

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 occurence of the ? character will be interpreted as a place for additional argument. If the literal character ? is required, 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 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.

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from_now(count, interval) View Source

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")

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.

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

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)

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.

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]]))

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.

Calculates the maximum for the given entry.

from p in Payment, select: max(p.value)
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merge(left_map, right_map) View Source

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.

Calculates the minimum for the given entry.

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

Unary not operation.

Binary or operation.

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.

Calculates the sum for the given entry.

from p in Payment, select: sum(p.value)
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type(interpolated_value, type) View Source

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)

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)