Item Path

Last modified 09 Feb 2022 16:38 +01:00
Table of Contents

Item path is a simple syntax for addressing properties, containers, references, attributes and similar items in prism data structures used in midPoint. I.e. it can address items in users, accounts, roles, assignments and in almost any midPoint data structure. The item path syntax is quite similar to XML XPath but it is much simpler. It is frequently used in mappings and expressions, search queries, etc.

The generic syntax of item path is as follows:

$variableName/segment[id]/segment[id]/....

The variableName and the [id] parts are optional. If variableName is not present then the path is assumed to be relative and its interpretation depends on the context in which it is used. If the id part is missing then it is assumed that there is only a single segment of such name or that the path addresses all the segments of that name (depends on context). Variable names and segment names are assumed to be QNames (see Namespaces section below).

The following table provides example paths and their meaning.

Path Meaning

$user/givenName

Property givenName in an object stored in variable user

$user/assignment[123]/description

Property description stored in the value of container assignment identified by id 123 which is in turn part of object stored in variable user

givenName

Property givenName stored in whatever object (or container value) assumed to be the current evaluation context

$user/activation

Container activation that belongs to object which is stored in variable user. It is assumed that user has only a single value of activation container.

$account/attributes/pir:shipName

Attribute shipName in the namespace defined by prefix pir which is part of value of container attributes that is part of an object stored in the variable account.

Variables

Variable definition may be used in the first segment of the item path (and only in the first segments). Variable name starts with a dollar sign ($). Variables are used in some situations, e.g. in mapping expressions, correlation and confirmation expressions, etc. The variable specification is optional. If not specified the path applies to appropriate default object which is usually a user or an account. Therefore the paths $user/fullName and fullName are often equivalent. Please see the documentation for a specific mapping or expression type to learn the details.

Variable content may be a primitive value or an object. If the content is a primitive value then only a simple path without any segment may be used. E.g. in such a case the $foo is a legal path but $foo/bar is not. If a variable contains an object (or a similar hierarchical structure) then also the segments may be used. E.g. $user/activation/administrativeStatus.

Namespaces

MidPoint supports full XML QNames (qualified names) in both the segment names and variable names. However since midPoint 3.0 the use of namespaces is optional. If the namespace part of the path is not present midPoint will try to determine it automatically. If the local part of the QName is unique in its respective scope then midPoint will use the path without raising any error or warning. This is the usual case. However there may be cases when the local part is not unique, e.g. in case that several conflicting midPoint extensions are used. Namespacing mechanism is used to resolve such conflicts.

Namespaces can be specified in the item path by using two mechanisms: internal and external. Both mechanisms are using namespace prefixes similar to XML and XPath.

Internal namespace definition is a part of path specification itself. The namespace declaration is provided before the actual path:

declare default namespace 'http://midpoint.evolveum.com/xml/ns/public/common/common-3';
fullName

This example defines a default namespace for the path. This means that every path component which does not have an explicit prefix is considered to be part of the specified namespace. In this case the fullName component is placed inside the http://midpoint.evolveum.com/xml/ns/public/common/common-3 namespace.

Internal namespace definition may also contain namespace prefix declaration:

declare namespace c="http://midpoint.evolveum.com/xml/ns/public/common/common-3";
declare namespace myext="http://my.com/whatever/";
$c:user/c:extension/myext:bar

This example defines prefix c for namespace http://midpoint.evolveum.com/xml/ns/public/common/common-3 and prefix myext for namespace http://my.com/whatever/. Each individual path part is then placed into appropriate namespace depending on which prefix was used.

Similar effect can be achieved by using external namespace declaration. In this case the item path retrieves prefix declarations from the enclosing document. Therefore the following example is equivalent to the previous example:

<path xmlns:c="http://midpoint.evolveum.com/xml/ns/public/common/common-3" xmlns:myext="http://my.com/whatever/">
  $c:user/c:extension/myext:bar
</path>

External declaration can be only used in data formats that support QNames - which practically means only XML. It cannot be used in simple languages such as JSON.

Use of namespaces in the path expressions

It is reasonably safe not to use namespaces in the item paths if you are deploying a specific solution. In this case you have the environment under control. You know what extensions are applied. You can check whether a specific path is unique or not. And in case that the path is not unique you can add namespaces on demand.

However, it is strongly recommended to use namespaces if you are building general-purpose midPoint extension or integrating a general-purpose product to midPoint. In such a case you do not have the final environment under control and you cannot predict what extensions will be used in such environment. Therefore, it is recommended to use full namespaces in this case to avoid conflicts with other extensions or products.
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