Bind parameters

AQL supports the usage of bind parameters, thus allowing to separate the query text from literal values used in the query. It is good practice to separate the query text from the literal values because this will prevent (malicious) injection of keywords and other collection names into an existing query. This injection would be dangerous because it may change the meaning of an existing query.

Using bind parameters, the meaning of an existing query cannot be changed. Bind parameters can be used everywhere in a query where literals can be used.

Syntax

The general syntax for bind parameters is @name where @ signifies that this is a value bind parameter and name is the actual parameter name. It can be used to substitute values in a query.

RETURN @value

For collections, there is a slightly different syntax @@coll where @@ signifies that it is a collection bind parameter and coll is the parameter name.

FOR doc IN @@coll
  RETURN doc

Keywords and other language constructs cannot be replaced by bind values, such as FOR, FILTER, IN, INBOUND or function calls.

Bind parameter names must start with any of the letters a to z (upper or lower case) or a digit (0 to 9), and can be followed by any letter, digit or the underscore symbol.

They must not be quoted in the query code:

FILTER u.name == "@name" // wrong
FILTER u.name == @name   // correct

FOR doc IN "@@collection" // wrong
FOR doc IN @@collection   // correct

If you need to do string processing (concatenation, etc.) in the query, you need to use string functions to do so:

FOR u IN users
  FILTER u.id == CONCAT('prefix', @id, 'suffix') && u.name == @name
  RETURN u

Usage

General

The bind parameter values need to be passed along with the query when it is executed, but not as part of the query text itself. In the web interface, there is a pane next to the query editor where the bind parameters can be entered. For below query, two input fields will show up to enter values for the parameters id and name.

FOR u IN users
  FILTER u.id == @id && u.name == @name
  RETURN u

When using db._query() (in arangosh for instance), then an object of key-value pairs can be passed for the parameters. Such an object can also be passed to the HTTP API endpoint _api/cursor, as attribute value for the key bindVars:

{
  "query": "FOR u IN users FILTER u.id == @id && u.name == @name RETURN u",
  "bindVars": {
    "id": 123,
    "name": "John Smith"
  }
}

Bind parameters that are declared in the query must also be passed a parameter value, or the query will fail. Specifying parameters that are not declared in the query will result in an error too.

Specific information about parameters binding can also be found in:

• AQL with Web Interface
• AQL with arangosh
• HTTP Interface for AQL Queries

Nested attributes

Bind parameters can be used for both, the dot notation as well as the square bracket notation for sub-attribute access. They can also be chained:

LET doc = { foo: { bar: "baz" } }

RETURN doc.@attr.@subattr
// or
RETURN doc[@attr][@subattr]

{
  "attr": "foo",
  "subattr": "bar"
}

Both variants in above example return [ "baz" ] as query result.

The whole attribute path, for highly nested data in particular, can also be specified using the dot notation and a single bind parameter, by passing an array of strings as parameter value. The elements of the array represent the attribute keys of the path:

LET doc = { a: { b: { c: 1 } } }
RETURN doc.@attr

{ "attr": [ "a", "b", "c" ] }

The example query returns [ 1 ] as result. Note that { "attr": "a.b.c" } would return the value of an attribute called a.b.c, not the value of attribute c with the parents a and b as [ "a", "b", "c" ] would.

Collection bind parameters

A special type of bind parameter exists for injecting collection names. This type of bind parameter has a name prefixed with an additional @ symbol, so @@name in the query.

FOR u IN @@collection
  FILTER u.active == true
  RETURN u

The second @ will be part of the bind parameter name, which is important to remember when specifying the bindVars (note the leading @):

{
  "query": "FOR u IN @@collection FILTER u.active == true RETURN u",
  "bindVars": {
    "@collection": "users"
  }
}