petrol 1.0.0 · OCaml Package

Provides an SQL E-DSL for writing well-typed SQL expressions.

type 'a t

'a t represents an SQL expression that produces a value corresponding to the type 'a.

type 'a expr_list =

| [] : unit expr_list
| :: : ('a t * 'b expr_list) -> ('a * 'b) expr_list

Represents a heterogeneous sequence of SQL expressions.

Note Provided you have opened the Expr module, you can use List syntax to construct such lists:

Petrol.Expr.[i 1; bl false]
(* - : (int * (bool * ())) Petrol.Expr.expr_list *)

type wrapped_assign

An opaque wrapper that represents an assignment of a value to a particular field in a table.

val pp : Stdlib.Format.formatter -> 'a t -> unit

pp fmt expr pretty prints an SQL expression as a string that can be parsed by an SQL engine.

Constants

The following functions define constant value expressions.

Note For each type, there are two flavours of constant expression: variable and static.

The key difference between the two is in terms of how they are represented in the final SQL query - in particular, variable constant expressions are encoded as holes (?) in the query, to which a constant value is supplied, whereas static constant expressions are encoded directly in the query string.

As Petrol functions cache the construction of SQL queries by their final string representation, you should prefer the dynamic form if you expect the constant value to change frequently - for example, if it is a constant value that you are receiving from elsewhere. Use the static form if you know that the value doesn't change and will always be the same.

val i : int -> int t

i v returns an expression that evaluates to the integer value v.

val f : float -> float t

f v returns an expression that evaluates to the real value v.

val s : string -> string t

s v returns an expression that evaluates to the string value v.

val b : string -> string t

b v returns an expression that evaluates to the bytes value v.

val bl : bool -> bool t

bl v returns an expression that evaluates to the bool value v.

val i_stat : int -> int t

i_stat v returns a static expression that evaluates to the integer value v.

val f_stat : float -> float t

f_stat v returns a static expression that evaluates to the real value v.

val s_stat : string -> string t

s_stat v returns a static expression that evaluates to the string value v.

val b_stat : string -> string t

b_stat v returns a static expression that evaluates to the bytes value v.

val true_ : bool t

true_ represents the SQL constant TRUE.

val false_ : bool t

false_ represents the SQL constant FALSE.

Book-keeping: Types, Naming, Nulls

val as_ : 'a t -> name:string -> 'a t * 'a t

as_ exp ~name returns a tuple (exp',exp'_ref) where exp' is the SQL expression exp AS name that names exp as name, and exp'_ref is simply name.

val nullable : 'a t -> 'a option t

nullable e encodes the fact that the expression e may return NULL.

val is_not_null : 'a t -> bool t

is_not_null e constructs an SQL expression that is TRUE iff the expression e is not NULL and FALSE otherwise.

val coerce : 'a t -> 'b Type.t -> 'b t

coerce expr ty coerces expression expr to the type ty. This coercion is not checked, so make sure you know what you're doing or it could fail at runtime.

val (:=) : 'a t -> 'a t -> wrapped_assign

v := expr returns an SQL expression that can be used with an update or insert clause to change the values in the database.

Operators

val (+) : int t -> int t -> int t

val (-) : int t -> int t -> int t

val (=) : 'a t -> 'a t -> bool t

val (<>) : 'a t -> 'a t -> bool t

val (<=) : 'a t -> 'a t -> bool t

val (<) : 'a t -> 'a t -> bool t

val (>) : 'a t -> 'a t -> bool t

val (>=) : 'a t -> 'a t -> bool t

val (&&) : bool t -> bool t -> bool t

val (||) : bool t -> bool t -> bool t

Functions

val count : ?distinct:bool -> 'a expr_list -> int t

val count_star : int t

val max : ?distinct:bool -> int t -> int t

val min : ?distinct:bool -> int t -> int t

val sum : ?distinct:bool -> int t -> int t

val total : ?distinct:bool -> int t -> int t

val group_concat : ?distinct:bool -> ?sep_by:string t -> string t -> string t

val abs : int t -> int t

val changes : int t

val glob : pat:string t -> string t -> bool t

val coalesce : 'a t list -> 'a t

val like : string t -> pat:string t -> bool t

val max_of : int t list -> int t

val min_of : int t list -> int t

val random : int t

val lower : string t -> string t

val upper : string t -> string t

package petrol

Constants

Book-keeping: Types, Naming, Nulls

Operators

Functions