AssertCondition policy

This page applies to Apigee and Apigee hybrid.

View Apigee Edge documentation.

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Overview

The AssertCondition policy evaluates a conditional statement at runtime in the request or response flows. You can define a condition based on the flow variables, and use this policy to assert the condition. A condition always evaluates to a boolean value, either true or false. For more information about writing a conditional statement, see Conditions reference.

After evaluating the condition, the AssertCondition policy stores the result of the evaluation in the assertcondition.policy-name.truthValue flow variable. You can use the resultant flow variable in your subsequent callouts or orchestrated logic. If a condition evaluates to true, the value of the variable is set to true, false otherwise. If you have defined multiple AssertCondition policies, the policy-name in the variable name helps you to uniquely identify the variable.

This policy is a Standard policy and can be deployed to any environment type. Not all users need to know about policy and environment types. For information on policy types and availability with each environment type, see Policy types.

`<AssertCondition>`

Defines an <AssertCondition> policy. By using this policy, you can evaluate a conditional statement that has one or more conditions joined by a logical operator. For information about all the supported operators in a condition, see Operators.

The result of a conditional statement is a boolean which can be either a true or a false.

Default Value	N/A
Required?	Required
Type	Complex type
Parent Element	N/A
Child Elements	`<Condition>` `<DisplayName>`

The following table provides a high-level description of the child elements of <AssertCondition>:

Child Element	Required?	Description
`<Condition>`	Yes	Specifies the condition to evaluate.
`<DisplayName>`	Optional	A custom name for the policy.

The <AssertCondition> element uses the following syntax:

Syntax

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<AssertCondition">
    <!-- Display name for this policy -->
    <DisplayName>DISPLAY_NAME</DisplayName>
    <!-- Assertion's condition where operators are defined -->
    <Condition>CONDITIONAL_STATEMENT</Condition>
</AssertCondition>

Example

The following example checks if the google.dialogflow.my-prefix.claimAmount variable is greater than 0 and less than 1000.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<AssertCondition continueOnError="false" enabled="true"
        name="MyAssertCondition">
    <DisplayName>Assert My Condition</DisplayName>
    <Condition>(google.dialogflow.my-prefix.claimAmount > 0)
                and
               (google.dialogflow.my-prefix.claimAmount LesserThan 1000)</Condition>
</AssertCondition>

In this example:

If the value of google.dialogflow.my-prefix.claimAmount variable is 500, the condition evaluates to true and hence the assertcondition.MyAssertCondition.truthValue variable is set to true.
However, if the value of the google.dialogflow.my-prefix.claimAmount variable is 1200, the assertcondition.MyAssertCondition.truthValue variable is set to false.

This element has the following attributes that are common to all policies:

Attribute	Default	Required?	Description
`name`	N/A	Required	The internal name of the policy. The value of the `name` attribute can contain letters, numbers, spaces, hyphens, underscores, and periods. This value cannot exceed 255 characters. Optionally, use the `<DisplayName>` element to label the policy in the management UI proxy editor with a different, natural-language name.
`continueOnError`	false	Optional	Set to `false` to return an error when a policy fails. This is expected behavior for most policies. Set to `true` to have flow execution continue even after a policy fails. See also: Fault rules are triggered ONLY in an error state (about continueOnError) Handling faults within the current flow
`enabled`	true	Optional	Set to `true` to enforce the policy. Set to `false` to turn off the policy. The policy will not be enforced even if it remains attached to a flow.
`async`	false	Deprecated	This attribute is deprecated.

Child element reference

This section describes the child elements of <AssertCondition>.

`<Condition>`

Specifies the condition to evaluate. For more information about writing a conditional statement in Apigee, see Conditions reference.

Default Value	N/A
Required?	Required
Type	String
Parent Element	`<AssertCondition>`
Child Elements	None

`<DisplayName>`

Use in addition to the name attribute to label the policy in the management UI proxy editor with a different, more natural-sounding name.

The <DisplayName> element is common to all policies.

Default Value	N/A
Required?	Optional. If you omit `<DisplayName>`, the value of the policy's `name` attribute is used.
Type	String
Parent Element	<`PolicyElement`>
Child Elements	None

The <DisplayName> element uses the following syntax:

Syntax

<PolicyElement>
  <DisplayName>POLICY_DISPLAY_NAME</DisplayName>
  ...
</PolicyElement>

Example

<PolicyElement>
  <DisplayName>My Validation Policy</DisplayName>
</PolicyElement>

The <DisplayName> element has no attributes or child elements.

Error codes

This section describes the fault codes and error messages that are returned and fault variables that are set by Apigee when this policy triggers an error. This information is important to know if you are developing fault rules to handle faults. To learn more, see What you need to know about policy errors and Handling faults.

Runtime errors

These errors can occur when the policy executes.

Fault code	HTTP status	Cause
`steps.assertcondition.ConditionEvaluationFailed`	`500`	Failed to evaluate the conditional statement. There can be many reasons for this error, including incorrect values in the variables at run time.

Deployment errors

These errors can occur when you deploy a proxy containing this policy.

Error name	Cause
`InvalidCondition`	The policy was not able to validate the conditional statement. There can be many reasons for this error, including malformed conditions or use of unsupported operators.

Fault variables

Whenever there are execution errors in a policy, Apigee generates error messages. You can view these error messages in the error response. Many a time, system generated error messages might not be relevant in the context of your product. You might want to customize the error messages based on the type of error to make the messages more meaningful.

To customize the error messages, you can use either fault rules or the RaiseFault policy. For information about differences between fault rules and the RaiseFault policy, see FaultRules vs. the RaiseFault policy. You must check for conditions using the Condition element in both the fault rules and the RaiseFault policy. Apigee provides fault variables unique to each policy and the values of the fault variables are set when a policy triggers runtime errors. By using these variables, you can check for specific error conditions and take appropriate actions. For more information about checking error conditions, see Building conditions.

The following table describes the fault variables specific to this policy.

Variables	Where	Example
`fault.name="FAULT_NAME"`	`FAULT_NAME` is the name of the fault, as listed in the Runtime errors table. The fault name is the last part of the fault code.	`fault.name Matches "ConditionEvaluationFailed"`
`AssertCondition.POLICY_NAME.failed`	`POLICY_NAME` is the user-specified name of the policy that threw the fault.	`AssertCondition.My-AssertCondition.failed = true`

For more information about policy errors, see What you need to know about policy errors.