Within a release pipeline a new Pull Requested is created using REST API.
How to link a specific (already existing) Work Item to the Pull Request using REST API?
In the current version (DevOps 2019) it is not supported to link Work Items using Pull Request API. (See also related community issue.)
Using PowerShell the following snipped may help.
$requestUri = "$tfsCollectionUri/$teamProject/_apis/wit/workitems/$workItemId?api-version=5.0"
$json = '
[ {
"op": "add",
"path": "/relations/-",
"value": {
"rel": "ArtifactLink",
"url": "$pullRequestArtifact",
"attributes": { "name": "pull request" }
}
} ]'
$response = Invoke-RestMethod -Uri $requestUri -UseDefaultCredentials -ContentType "application/json-patch+json" -Method Patch -Body $json
Note, $pullRequestArtifact
needs to be set. You can get it e.g. from get request.