functions/Mount-DbaDatabase.ps1

function Mount-DbaDatabase {
    <#
        .SYNOPSIS
            Attach a SQL Server Database - aliased to Attach-DbaDatabase
 
        .DESCRIPTION
            This command will attach a SQL Server database.
 
        .PARAMETER SqlInstance
            The SQL Server instance.
 
        .PARAMETER SqlCredential
            Login to the target instance using alternative credentials. Windows and SQL Authentication supported. Accepts credential objects (Get-Credential)
 
        .PARAMETER Database
            The database(s) to attach.
 
        .PARAMETER FileStructure
            A StringCollection object value that contains a list database files. If FileStructure is not specified, BackupHistory will be used to guess the structure.
 
        .PARAMETER DatabaseOwner
            Sets the database owner for the database. The sa account (or equivalent) will be used if DatabaseOwner is not specified.
 
        .PARAMETER AttachOption
            An AttachOptions object value that contains the attachment options. Valid options are "None", "RebuildLog", "EnableBroker", "NewBroker" and "ErrorBrokerConversations".
 
        .PARAMETER WhatIf
            If this switch is enabled, no actions are performed but informational messages will be displayed that explain what would happen if the command were to run.
 
        .PARAMETER Confirm
            If this switch is enabled, you will be prompted for confirmation before executing any operations that change state.
 
        .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: Database
            Website: https://dbatools.io
            Copyright: (C) Chrissy LeMaire, clemaire@gmail.com
            License: MIT https://opensource.org/licenses/MIT
 
        .LINK
            https://dbatools.io/Mount-DbaDatabase
 
        .EXAMPLE
            $fileStructure = New-Object System.Collections.Specialized.StringCollection
            $fileStructure.Add("E:\archive\example.mdf")
            $filestructure.Add("E:\archive\example.ldf")
            $filestructure.Add("E:\archive\example.ndf")
            Mount-DbaDatabase -SqlInstance sql2016 -Database example -FileStructure $fileStructure
 
            Attaches a database named "example" to sql2016 with the files "E:\archive\example.mdf", "E:\archive\example.ldf" and "E:\archive\example.ndf". The database owner will be set to sa and the attach option is None.
 
        .EXAMPLE
            Mount-DbaDatabase -SqlInstance sql2016 -Database example
 
            Since the FileStructure was not provided, this command will attempt to determine it based on backup history. If found, a database named example will be attached to sql2016.
 
        .EXAMPLE
            Mount-DbaDatabase -SqlInstance sql2016 -Database example -WhatIf
 
            Shows what would happen if the command were executed (without actually performing the command)
    #>

    [CmdletBinding(SupportsShouldProcess)]
    Param (
        [parameter(Mandatory, ValueFromPipeline)]
        [Alias("ServerInstance", "SqlServer")]
        [DbaInstanceParameter[]]$SqlInstance,
        [PSCredential]
        $SqlCredential,
        [parameter(Mandatory)]
        [string[]]$Database,
        [System.Collections.Specialized.StringCollection]$FileStructure,
        [string]$DatabaseOwner,
        [ValidateSet('None', 'RebuildLog', 'EnableBroker', 'NewBroker', 'ErrorBrokerConversations')]
        [string]$AttachOption = "None",
        [Alias('Silent')]
        [switch]$EnableException
    )
    process {
        foreach ($instance in $SqlInstance) {
            try {
                $server = Connect-SqlInstance -SqlInstance $instance -SqlCredential $sqlcredential
            }
            catch {
                Stop-Function -Message "Failure" -Category ConnectionError -ErrorRecord $_ -Target $instance -Continue
            }

            if (-not $server.Logins.Item($DatabaseOwner)) {
                try {
                    $DatabaseOwner = ($server.Logins | Where-Object { $_.id -eq 1 }).Name
                }
                catch {
                    $DatabaseOwner = "sa"
                }
            }

            foreach ($db in $database) {

                if ($server.Databases[$db]) {
                    Stop-Function -Message "$db is already attached to $server." -Target $db -Continue
                }

                if ($server.Databases[$db].IsSystemObject) {
                    Stop-Function -Message "$db is a system database and cannot be attached using this method." -Target $db -Continue
                }

                if (-Not (Test-Bound -Parameter FileStructure)) {
                    $backuphistory = Get-DbaBackupHistory -SqlInstance $server -Database $db -Type Full | Sort-Object End -Descending | Select-Object -First 1

                    if (-not $backuphistory) {
                        $message = "Could not enumerate backup history to automatically build FileStructure. Rerun the command and provide the filestructure parameter."
                        Stop-Function -Message $message -Target $db -Continue
                    }

                    $backupfile = $backuphistory.Path[0]
                    $filepaths = (Read-DbaBackupHeader -SqlInstance $server -FileList -Path $backupfile).PhysicalName

                    $FileStructure = New-Object System.Collections.Specialized.StringCollection
                    foreach ($file in $filepaths) {
                        $exists = Test-DbaSqlpath -SqlInstance $server -Path $file
                        if (-not $exists) {
                            $message = "Could not find the files to build the FileStructure. Rerun the command and provide the FileStructure parameter."
                            Stop-Function -Message $message -Target $file -Continue
                        }

                        $null = $FileStructure.Add($file)
                    }
                }

                If ($Pscmdlet.ShouldProcess($server, "Attaching $Database with $DatabaseOwner as database owner and $AttachOption as attachoption")) {
                    try {
                        $server.AttachDatabase($db, $FileStructure, $DatabaseOwner, [Microsoft.SqlServer.Management.Smo.AttachOptions]::$AttachOption)

                        [pscustomobject]@{
                            ComputerName  = $server.ComputerName
                            InstanceName  = $server.ServiceName
                            SqlInstance   = $server.DomainInstanceName
                            Database      = $db
                            AttachResult  = "Success"
                            AttachOption  = $AttachOption
                            FileStructure = $FileStructure
                        }
                    }
                    catch {
                        Stop-Function -Message "Failure" -ErrorRecord $_ -Target $server
                    }
                }
            }
        }
    }
}