Crate diesel[][src]

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Diesel is an ORM and query builder designed to reduce the boilerplate for database interactions. If this is your first time reading this documentation, we recommend you start with the getting started guide. We also have many other long form guides.

Where to find things

Declaring your schema

For Diesel to validate your queries at compile time it requires you to specify your schema in your code, which you can do with the table! macro. diesel print-schema or infer_schema! can be used to automatically generate these macro calls (by connecting to your database and querying its schema).

Getting started

Queries usually start from either a table, or a function like update. Those functions can be found here.

Diesel provides a prelude module, which exports most of the typically used traits and types. We are conservative about what goes in this module, and avoid anything which has a generic name. Files which use Diesel are expected to have use diesel::prelude::*;.

Constructing a query

The tools the query builder gives you can be put into these three categories:

  • “Query builder methods” are things that map to portions of a whole query (such as ORDER and WHERE). These methods usually have the same name as the SQL they map to, except for WHERE which is called filter in Diesel (To not conflict with the Rust keyword). These methods live in the query_dsl module.
  • “Expression methods” are things you would call on columns or other individual values. These methods live in the expression_methods module You can often find these by thinking “what would this be called” if it were a method and typing that into the search bar (e.g. LIKE is called like in Diesel). Most operators are named based on the Rust function which maps to that operator in std::ops (For example == is called .eq, and != is called .ne).
  • “Bare functions” are normal SQL functions such as sum. They live in the dsl module. Diesel only supports a very small number of these functions. You can declare additional functions you want to use with the sql_function! macro.

Serializing and Deserializing

Types which represent the result of a SQL query implement a trait called Queryable.

Diesel maps “Rust types” (e.g. i32) to and from “SQL types” (e.g. diesel::sql_types::Integer). You can find all the types supported by Diesel in the sql_types module. These types are only used to represent a SQL type. You should never put them on your Queryable structs.

To find all the Rust types which can be used with a given SQL type, see the documentation for that SQL type.

To find all the SQL types which can be used with a Rust type, go to the docs for either ToSql or FromSql, go to the “Implementors” section, and find the Rust type you want to use.

Getting help

If you run into problems, Diesel has a very active Gitter room. You can come ask for help at


pub use prelude::*;
pub use result::Error::NotFound;


Traits related to relationships between multiple tables.

Types which represent various database backends

Types related to database connections

Structs to represent the primitive equivalent of SQL types where there is no existing Rust primitive, or where using it would be confusing (such as date and time types). This module will re-export all backend specific data structures when compiled against that backend.

Types and traits related to deserializing values from the database

Includes various helper types and bare functions which are named too generically to be included in prelude, but are often used when using Diesel.

AST types representing various typed SQL expressions.

Adds various methods to construct new expressions. These traits are exported by default, and implemented automatically.

Provide helper types for concisely writing the return type of functions. As with iterators, it is unfortunately difficult to return a partially constructed query without exposing the exact implementation of the function. Without higher kinded types, these various DSLs can’t be combined into a single trait for boxing purposes.

Representation of migrations

Provides types and functions related to working with MySQL

Provides types and functions related to working with PostgreSQL

Re-exports important traits and types. Meant to be glob imported when using Diesel.

Contains traits responsible for the actual construction of SQL statements

Traits that construct SELECT statements

Types related to describing schema, and interactions between tables.

Connection pooling via r2d2.

Errors, type aliases, and functions related to working with Result.

Contains the Row trait

Types and traits related to serializing values for the database

Types which represent a SQL data type.

Provides types and functions related to working with SQLite


Allow two or more tables which are otherwise unrelated to be used together in a query.

Useful for libraries adding support for new SQL types. Apps should never need to call this.

Useful for libraries adding support for new SQL types. Apps should never need to call this.

Useful for libraries adding support for new SQL types. Apps should never need to call this.

Allow two tables to be referenced in a join query without providing an explicit ON clause.

Declare a 0 argument SQL function for use in your code. This will generate a unit struct, which is an expression representing calling this function. See now for example output. now was generated using:

Gets the value out of an option, or returns an error.

Indicates that an expression allows all numeric operators. If you create new SQL functions that return a numeric type, you should invoke this macro that type. Unfortunately, Rust disallows us from automatically implementing Add for types which implement Expression, under its orphan rules.

Implements the Rust operator for a given type. If you create a new SQL function, which returns a type that you’d like to use an operator on, you should invoke this macro. Unfortunately, Rust disallows us from automatically implementing Add and other traits from std::ops, under its orphan rules.

Declare a sql function for use in your code.

Specifies that a table exists, and what columns it has. This will create a new public module, with the same name, as the name of the table. In this module, you’ll find a unit struct named table, and a unit struct with the names of each of the columns.


Takes a query QueryFragment expression as an argument and returns a type that implements fmt::Display and fmt::Debug to show the query.

Creates a DELETE statement.

Creates an INSERT statement for the target table.

Creates an INSERT [OR] IGNORE statement.

Creates a REPLACE statement.

Creates a bare select statement, with no from clause. Primarily used for testing diesel itself, but likely useful for third party crates as well. The given expressions must be selectable from anywhere.

Construct a full SQL query using raw SQL.

Creates an UPDATE statement.