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To enable it, being logged as Jira administrator click on cog icon (1), then access "Issues" (2):
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On a newly loaded screen find "Custom fields" (3) and access it.
In an opened prompt click "All" (1) and type "cascading contact select" in the search box (2). After you find it click on it (3) and press "Next" (4) button.
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On a next screen provide name and description and hit "Create":
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Then, as presented below, tick projects' screens in which you wish to see new custom field to be present:
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After you select everything as desired, press "Update" button.
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Now, directly after doing so, when you create a new Jira issue, at the bottom of the prompt, you can see "Contacts" custom field:
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There's a possibility to select from company name and its members (1) - all entered details are visible next to it as well. If contact doesn't exist, or needs amendments, it can be quickly accessed and edited by using a button on a right hand side of it (2). View will switch to the same as presented here.
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When you open such issue and click on "Contacts" name (1) you will be presented with JQL query search results containing list of all issues where company name is as presented below. If you need to send an email using third party software like MS Outlook, you may also find useful that listed email enables to do so, after clicking on it (2).
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JQL query can be modified manually to find only those issues containing interesting aspects i.e.one of contact's member name - after clicking provided contacts name feel free to modify it in Jira to get more accurate search results.
There's a way to include two or more contacts in a single issue in Jira - to do so please install Admin Tools for Jira and follow this guide. After cloning same custom field as used by default in Contacts Manager, you will be able to tie it to the same (i.e. as presented above) screens and as a result you can expect to see more contacts within a single Jira issue. If you prefer to do it without the help of mentioned add-on simply again follow the presented on this page procedure and name "Cascading Contact Select" using different name than originally created, then tie it with the same screens as an original one. As a result you can expect to see:
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Cross-company entries are also possible:
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