
= Regex Property Extender
:description: Regex property extender in {page-component-title} specializes in importing a string property from a resource table.

The Regex property extender works similarly to the xref:deep-dive/performance-data-collection/snmp-property-extenders/index-split.adoc[Index Split] extender, with the added capability of importing a string property from a source table.

This is useful when some portion of the target MIB table's index can be used as an index in the source MIB table.
For example, the Cisco Airespace `bsnAPIfLoadParametersTable` is indexed using the tuple of `bsnAPDot3MacAdddress` and `bsnAPIfSlotId`, whereas the `bsnAPTable` is indexed on `bsnAPDot3MacAddress` alone.

....
bsnAPIfLoadParametersEntry OBJECT-TYPE
    -- ...
    DESCRIPTION
        "An entry (conceptual row) in the Table.
        Entries in this MIB are indexed by
        bsnAPDot3MacAddress and bsnAPIfSlotId"
    INDEX           {
                        bsnAPDot3MacAddress,
                        bsnAPIfSlotId
                    } <1>

    -- ...

bsnAPEntry OBJECT-TYPE
    -- ...
    DESCRIPTION
        "An entry in the bsnAPTable."
    INDEX           { bsnAPDot3MacAddress } <2>
    -- ...
....
<1> `bsnAPDot3MacAddress` is the first component of the compound index for the entry type for `bsnAPIfLoadParametersTable`.
<2> `bsnAPDot3MacAddress` is the sole index for the entry type for `bsnAPTable`.

By extracting only the first index component and using the result as an index into the source MIB table, it's possible to import the human-readable `bsnAPName` string property from the source MIB table.

== Configuration

The Regex property extender expects three parameters, all of which are required:

[options="autowidth"]
|===
| Name  | Description

| source-type
| The name of the `resourceType` associated with the source MIB table.

| source-alias
| The alias name of the string property to import from the source MIB table.

| index-pattern
| A regular expression containing one matching group.
|===

The `index-pattern` expression must meet the same criteria as for the Index Split property extender.
The subpattern matched by its first capturing group will be used as an index into the source MIB table; any further groups are ignored.

The following example shows how to use the value of `bsnAPDot3MacAddress` as an index into the `bsnAPTable`:

[source, xml]
----
<resourceType name="bsnAPEntry" label="Cisco Wireless AP" resourceLabel="${bsnAPName} (index ${index})">
  <persistenceSelectorStrategy class="org.opennms.netmgt.collection.support.PersistAllSelectorStrategy" />
  <storageStrategy class="org.opennms.netmgt.collection.support.IndexStorageStrategy" />
</resourceType>

<resourceType name="bsnAPIfLoadParametersEntry" label="Cisco Wireless AP Resources" resourceLabel="${bsnAPName} (index ${index})">
  <persistenceSelectorStrategy class="org.opennms.netmgt.collection.support.PersistAllSelectorStrategy" />
  <storageStrategy class="org.opennms.netmgt.collection.support.IndexStorageStrategy" />
</resourceType>

<groups>
  <group name="bsnAPTable" ifType="all">
    <mibObj oid=".1.3.6.1.4.1.14179.2.2.1.1.3" instance="bsnAPEntry" alias="bsnAPName" type="string" /> <1>
  </group>

  <group name="bsnAPIfLoadParametersTable" ifType="all">
    <mibObj oid=".1.3.6.1.4.1.14179.2.2.13.1.4" instance="bsnAPIfLoadParametersEntry" alias="bsnAPIfLoadNumOfCli" type="integer" />
    <property instance="bsnAPIfLoadParametersEntry" alias="bsnAPName" class-name="org.opennms.netmgt.collectd.RegExPropertyExtender"> <2>
      <parameter key="source-type" value="bsnAPEntry" />
      <parameter key="source-alias" value="bsnAPName" />
      <parameter key="index-pattern" value="^(.+)\.\d+$" /> <3>
    </property>
  </group>
</groups>
----
<1> Regular string property `bsnAPName` on the source table.
<2> Extended string property `bsnAPName` on the target table.
<3> Regular expression; the portion in parentheses is what gets extracted.
`\d+` means "one or more decimal digit characters".
