This page describes the XML elements comprising the FreezeScript inspection descriptors.

On this page:

<dumpdb> Descriptor Element

The top-level descriptor in a descriptor file. It requires one child descriptor, <database>, and supports any number of <dump> descriptors. This descriptor has no attributes.

<database> Descriptor Element

The attributes of this descriptor define the key and value types of the database. It supports any number of child descriptors, but at most one <record> descriptor. The <database> descriptor also creates a global scope for user-defined symbols.

The attributes supported by the <database> descriptor are described in the following table:

As an example, consider the following <database> descriptor. In this case, the Freeze map to be examined has key type int and value type ::Employee:

{zcode:xml}
<database key="int" value="::Employee">
{zcode}

<record> Descriptor Element

Commences the database traversal. Child descriptors are executed for each record in the database, but after any <dump> descriptors are executed. The <record> descriptor introduces the read-only symbols key, value and facet into a local scope. These symbols are accessible to child descriptors, but not to <dump> descriptors. The facet symbol is a string indicating the facet name of the object in the current record, and is only relevant for Freeze evictor databases.

Note that database traversal only occurs if a <record> descriptor is present.

<dump> Descriptor Element

Executed for all instances of a Slice type. Only one <dump> descriptor can be specified for a type, but a <dump> descriptor is not required for every type. The read-only symbol value is introduced into a local scope. The attributes supported by this descriptor are described in the following table:

Below is an example of a <dump> descriptor that searches for certain products:

{zcode:xml}
<dump type="::Product">
    <if test="value.description.find('scanner') != -1">
        <echo message="Scanner SKU: " value="value.SKU"/>
    </if>
</dump>
{zcode}

For class types, dumpdb first attempts to locate a <dump> descriptor for the object's most-derived type. If no descriptor is found, dumpdb proceeds up the class hierarchy in an attempt to find a descriptor. The base object type, Object, is the root of every class hierarchy and is included in the search for descriptors. It is therefore possible to define a <dump> descriptor for type Object, which will be invoked for every class instance.

Note that <dump> descriptors are executed recursively. For example, consider the following Slice definitions:

{zcode:slice}
struct Inner {
    int sum;
};
struct Outer {
    Inner i;
};
{zcode}

When dumpdb is interpreting a value of type Outer, it executes the <dump> descriptor for Outer, then recursively executes the <dump> descriptor for the Inner member, but only if the contents attribute of the Outer descriptor has the value true.

<iterate> Descriptor Element

Iterates over a dictionary or sequence, executing child descriptors for each element. The symbol names selected to represent the element information may conflict with existing symbols in the enclosing scope, in which case those outer symbols are not accessible to child descriptors. The attributes supported by this descriptor are described in the following table:

Shown below is an example of an <iterate> descriptor that displays the name of an employee if the employee's salary is greater than $3000.

{zcode:xml}
<iterate target="value.employeeMap" key="id" value="emp">
    <if test="emp.salary > 3000">
        <echo message="Employee: " value="emp.name"/>
    </if>
</iterate>
{zcode}

<if> Descriptor Element

Conditionally executes child descriptors. The attributes supported by this descriptor are described in the following table:

Child descriptors are executed if the expression in test evaluates to true.

<set> Descriptor Element

Modifies a value. The value and type attributes are mutually exclusive. If target denotes a dictionary element, that element must already exist (i.e., <set> cannot be used to add an element to a dictionary). The attributes supported by this descriptor are described in the following table:

The <set> descriptor below modifies a member of a dictionary element:

{zcode:xml}
<set target="new.parts['P105J3'].cost" value="new.parts['P105J3'].cost * 1.05"/>
{zcode}

This <set> descriptor adds an element to a sequence and initializes its value:

{zcode:xml}
<set target="new.partsList" length="new.partsList.length + 1" value="'P105J3'"/>
{zcode}

<add> Descriptor Element

Adds a new element to a sequence or dictionary. It is legal to add an element while traversing the sequence or dictionary using <iterate>, however the traversal order after the addition is undefined. The key and index attributes are mutually exclusive, as are the value and type attributes. If neither value nor type is specified, the new element is initialized with a default value. The attributes supported by this descriptor are described in the following table:

Below is an example of an <add> descriptor that adds a new dictionary element and then initializes its member:

{zcode:xml}
<add target="new.parts" key="'P105J4'"/>
<set target="new.parts['P105J4'].cost" value="3.15"/>
{zcode}

<define> Descriptor Element

Defines a new symbol in the current scope. The attributes supported by this descriptor are described in the following table:

Below are two examples of the <define> descriptor. The first example defines the symbol identity to have type Ice::Identity, and proceeds to initialize its members using <set>:

{zcode:xml}
<define name="identity" type="::Ice::Identity"/>
<set target="identity.name" value="steve"/>
<set target="identity.category" value="Admin"/>
{zcode}

The second example uses the enumeration we first saw in our discussion of custom database migration to define the symbol manufacturer and assign it a default value:

{zcode:xml}
<define name="manufacturer" type="::BigThree" value="::DaimlerChrysler"/>
{zcode}

<remove> Descriptor Element

Removes an element from a sequence or dictionary. It is legal to remove an element while traversing a sequence or dictionary using <iterate>, however the traversal order after removal is undefined. The attributes supported by this descriptor are described in the following table:

<fail> Descriptor Element

Causes transformation to fail immediately. If test is specified, transformation fails only if the expression evaluates to true. The attributes supported by this descriptor are described in the following table:

The following <fail> descriptor terminates the transformation if a range error is detected:

{zcode:xml}
<fail message="range error occurred in ticket count!" test="value.ticketCount > 32767"/>
{zcode}

<echo> Descriptor Element

Displays values and informational messages. If no attributes are specified, only a newline is printed. The attributes supported by this descriptor are described in the following table:

Shown below is an <echo> descriptor that uses both message and value attributes:

{zcode:xml}
<if test="value.ticketCount > 32767">
    <echo message="range error occurred in ticket count: " value="value.ticketCount"/>
</if>
{zcode}

See Also

• Freeze Maps
• Freeze Evictors
• Facets and Versioning
• Custom Database Migration
• FreezeScript Descriptor Expression Language