functions/Add-DbaAgDatabase.ps1

#ValidationTags#Messaging,FlowControl,Pipeline,CodeStyle#
function Add-DbaAgDatabase {
    <#
    .SYNOPSIS
        Adds a database to an availability group on a SQL Server instance.
 
    .DESCRIPTION
        Adds a database to an availability group on a SQL Server instance.
 
   .PARAMETER SqlInstance
        The target SQL Server instance or instances. Server version must be SQL Server version 2012 or higher.
 
    .PARAMETER SqlCredential
        Login to the SqlInstance instance using alternative credentials. Windows and SQL Authentication supported. Accepts credential objects (Get-Credential)
 
    .PARAMETER Database
        The database or databases to add.
 
    .PARAMETER AvailabilityGroup
        The availability group where the databases will be added.
 
    .PARAMETER InputObject
        Enables piping from Get-DbaDatabase, Get-DbaDbSharePoint and more.
 
    .PARAMETER WhatIf
        Shows what would happen if the command were to run. No actions are actually performed.
 
    .PARAMETER Confirm
        Prompts you for confirmation before executing any changing operations within the command.
 
    .PARAMETER EnableException
        By default, when something goes wrong we try to catch it, interpret it and give you a friendly warning message.
        This avoids overwhelming you with "sea of red" exceptions, but is inconvenient because it basically disables advanced scripting.
        Using this switch turns this "nice by default" feature off and enables you to catch exceptions with your own try/catch.
 
    .NOTES
        Tags: AvailabilityGroup, HA, AG
        Author: Chrissy LeMaire (@cl), netnerds.net
        Website: https://dbatools.io
        Copyright: (c) 2018 by dbatools, licensed under MIT
        License: MIT https://opensource.org/licenses/MIT
 
    .LINK
        https://dbatools.io/Add-DbaAgDatabase
 
    .EXAMPLE
        PS C:\> Add-DbaAgDatabase -SqlInstance sql2017a -AvailabilityGroup ag1 -Database db1, db2 -Confirm
 
        Adds db1 and db2 to ag1 on sql2017a. Prompts for confirmation.
 
    .EXAMPLE
        PS C:\> Get-DbaDatabase -SqlInstance sql2017a | Out-GridView -Passthru | Add-DbaAgDatabase -AvailabilityGroup ag1
 
        Adds selected databases from sql2017a to ag1
 
    .EXAMPLE
        PS C:\> Get-DbaDbSharePoint -SqlInstance sqlcluster | Add-DbaAgDatabase -AvailabilityGroup SharePoint
 
        Adds SharePoint databases as found in SharePoint_Config on sqlcluster to ag1 on sqlcluster
 
    .EXAMPLE
        PS C:\> Get-DbaDbSharePoint -SqlInstance sqlcluster -ConfigDatabase SharePoint_Config_2019 | Add-DbaAgDatabase -AvailabilityGroup SharePoint
 
        Adds SharePoint databases as found in SharePoint_Config_2019 on sqlcluster to ag1 on sqlcluster
#>

    [CmdletBinding(SupportsShouldProcess, ConfirmImpact = 'Low')]
    param (
        [DbaInstanceParameter[]]$SqlInstance,
        [PSCredential]$SqlCredential,
        [parameter(Mandatory)]
        [string]$AvailabilityGroup,
        [string[]]$Database,
        [parameter(ValueFromPipeline)]
        [Microsoft.SqlServer.Management.Smo.Database[]]$InputObject,
        [switch]$EnableException
    )
    process {
        if ((Test-Bound -ParameterName SqlInstance)) {
            if ((Test-Bound -Not -ParameterName Database) -or (Test-Bound -Not -ParameterName AvailabilityGroup)) {
                Stop-Function -Message "You must specify one or more databases and one Availability Groups when using the SqlInstance parameter."
                return
            }
        }

        foreach ($instance in $SqlInstance) {
            $InputObject += Get-DbaDatabase -SqlInstance $instance -SqlCredential $SqlCredential -Database $Database
        }

        foreach ($db in $InputObject) {
            $ags = Get-DbaAvailabilityGroup -SqlInstance $db.Parent -AvailabilityGroup $AvailabilityGroup

            foreach ($ag in $ags) {
                if ($Pscmdlet.ShouldProcess($ag.Parent.Name, "Adding availability group $db to $($db.Parent.Name)")) {
                    try {
                        $agdb = New-Object Microsoft.SqlServer.Management.Smo.AvailabilityDatabase($ag, $db.Name)
                        # something is up with .net create(), force a stop
                        Invoke-Create -Object $agdb
                        Get-DbaAgDatabase -SqlInstance $ag.Parent -Database $db.Name
                    } catch {
                        Stop-Function -Message "Failure" -ErrorRecord $_ -Continue
                    }
                }
            }
        }
    }
}