Set variable
APPLIES TO: All API Management tiers
The set-variable policy declares a context variable and assigns it a value specified via an expression or a string literal. If the expression contains a literal it will be converted to a string and the type of the value will be System.String.
Note
Set the policy's elements and child elements in the order provided in the policy statement. Learn more about how to set or edit API Management policies.
Policy statement
<set-variable name="variable name" value="Expression | String literal" />
Attributes
| Attribute | Description | Required |
|---|---|---|
| name | The name of the variable. Policy expressions aren't allowed. | Yes |
| value | The value of the variable. This can be an expression or a literal value. Policy expressions are allowed. | Yes |
Usage
- Policy sections: inbound, outbound, backend, on-error
- Policy scopes: global, workspace, product, API, operation
- Gateways: classic, v2, consumption, self-hosted, workspace
Allowed types
Expressions used in the set-variable policy must return one of the following basic types.
- System.Boolean
- System.SByte
- System.Byte
- System.UInt16
- System.UInt32
- System.UInt64
- System.Int16
- System.Int32
- System.Int64
- System.Decimal
- System.Single
- System.Double
- System.Guid
- System.String
- System.Char
- System.DateTime
- System.TimeSpan
- System.Byte?
- System.UInt16?
- System.UInt32?
- System.UInt64?
- System.Int16?
- System.Int32?
- System.Int64?
- System.Decimal?
- System.Single?
- System.Double?
- System.Guid?
- System.String?
- System.Char?
- System.DateTime?
Example
The following example demonstrates a set-variable policy in the inbound section. This set variable policy creates an isMobile Boolean context variable that is set to true if the User-Agent request header contains the text iPad or iPhone.
<set-variable name="IsMobile" value="@(context.Request.Headers.GetValueOrDefault("User-Agent","").Contains("iPad") || context.Request.Headers.GetValueOrDefault("User-Agent","").Contains("iPhone"))" />
Related policies
Related content
For more information about working with policies, see:
- Tutorial: Transform and protect your API
- Policy reference for a full list of policy statements and their settings
- Policy expressions
- Set or edit policies
- Reuse policy configurations
- Policy snippets repo
- Author policies using Microsoft Copilot in Azure