functions/Set-DbaDbOwner.ps1

function Set-DbaDbOwner {
    <#
    .SYNOPSIS
        Sets database owners with a desired login if databases do not match that owner.
 
    .DESCRIPTION
        This function will alter database ownership to match a specified login if their current owner does not match the target login. By default, the target login will be 'sa', but the function will allow the user to specify a different login for ownership. The user can also apply this to all databases or only to a select list of databases (passed as either a comma separated list or a string array).
 
        Best Practice reference: http://weblogs.sqlteam.com/dang/archive/2008/01/13/Database-Owner-Troubles.aspx
 
    .PARAMETER SqlInstance
        The target SQL Server instance or instances.
 
    .PARAMETER SqlCredential
        Login to the target instance using alternative credentials. Windows and SQL Authentication supported. Accepts credential objects (Get-Credential)
 
    .PARAMETER Database
        Specifies the database(s) to process. Options for this list are auto-populated from the server. If unspecified, all databases will be processed.
 
    .PARAMETER ExcludeDatabase
        Specifies the database(s) to exclude from processing. Options for this list are auto-populated from the server.
 
    .PARAMETER InputObject
        Enables piping from Get-DbaDatabase
 
    .PARAMETER TargetLogin
        Specifies the login that you wish check for ownership. This defaults to 'sa' or the sysadmin name if sa was renamed. This must be a valid security principal which exists on the target server.
 
    .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, Owner, DbOwner
        Author: Michael Fal (@Mike_Fal), http://mikefal.net
 
        Website: https://dbatools.io
        Copyright: (c) 2018 by dbatools, licensed under MIT
        License: MIT https://opensource.org/licenses/MIT
 
    .LINK
        https://dbatools.io/Set-DbaDbOwner
 
    .EXAMPLE
        PS C:\> Set-DbaDbOwner -SqlInstance localhost
 
        Sets database owner to 'sa' on all databases where the owner does not match 'sa'.
 
    .EXAMPLE
        PS C:\> Set-DbaDbOwner -SqlInstance localhost -TargetLogin DOMAIN\account
 
        Sets the database owner to DOMAIN\account on all databases where the owner does not match DOMAIN\account.
 
    .EXAMPLE
        PS C:\> Set-DbaDbOwner -SqlInstance sqlserver -Database db1, db2
 
        Sets database owner to 'sa' on the db1 and db2 databases if their current owner does not match 'sa'.
 
    .EXAMPLE
        PS C:\> $db = Get-DbaDatabase -SqlInstance localhost -Database db1, db2
        PS C:\> $db | Set-DbaDbOwner -TargetLogin DOMAIN\account
 
        Sets database owner to 'sa' on the db1 and db2 databases if their current owner does not match 'sa'.
 
    #>

    [CmdletBinding(SupportsShouldProcess)]
    param (
        [parameter(ValueFromPipeline)]
        [DbaInstanceParameter[]]$SqlInstance,
        [PSCredential]$SqlCredential,
        [object[]]$Database,
        [object[]]$ExcludeDatabase,
        [parameter(ValueFromPipeline)]
        [Microsoft.SqlServer.Management.Smo.Database[]]$InputObject,
        [Alias("Login")]
        [string]$TargetLogin,
        [switch]$EnableException
    )

    process {
        if (-not $InputObject -and -not $SqlInstance) {
            Stop-Function -Message "You must pipe in a database or specify a SqlInstance"
            return
        }

        if ($SqlInstance) {
            $InputObject += Get-DbaDatabase -SqlInstance $SqlInstance -SqlCredential $SqlCredential -Database $Database -ExcludeDatabase $ExcludeDatabase
        }

        foreach ($db in $InputObject) {
            # Exclude system databases
            if ($db.IsSystemObject) {
                continue
            }
            if (!$db.IsAccessible) {
                Write-Message -Level Warning -Message "Database $db is not accessible. Skipping."
                continue
            }

            $server = $db.Parent
            $instance = $server.Name

            # dynamic sa name for orgs who have changed their sa name
            if (!$TargetLogin) {
                $TargetLogin = ($server.logins | Where-Object { $_.id -eq 1 }).Name
            }

            #Validate login
            if (($server.Logins.Name) -notcontains $TargetLogin) {
                Stop-Function -Message "$TargetLogin is not a valid login on $instance. Moving on." -Continue -EnableException $EnableException
            }

            #Owner cannot be a group
            $TargetLoginObject = $server.Logins | where-object {$PSItem.Name -eq $TargetLogin }| Select-Object -property  Name, LoginType
            if ($TargetLoginObject.LoginType -eq 'WindowsGroup') {
                Stop-Function -Message "$TargetLogin is a group, therefore can't be set as owner. Moving on." -Continue -EnableException $EnableException
            }

            $dbname = $db.name
            if ($PSCmdlet.ShouldProcess($instance, "Setting database owner for $dbname to $TargetLogin")) {
                try {
                    Write-Message -Level Verbose -Message "Setting database owner for $dbname to $TargetLogin on $instance."
                    # Set database owner to $TargetLogin (default 'sa')
                    # Ownership validations checks

                    if ($db.Status -notmatch 'Normal') {
                        Write-Message -Level Warning -Message "$dbname on $instance is in a $($db.Status) state and can not be altered. It will be skipped."
                    }
                    #Database is updatable, not read-only
                    elseif ($db.IsUpdateable -eq $false) {
                        Write-Message -Level Warning -Message "$dbname on $instance is not in an updateable state and can not be altered. It will be skipped."
                    }
                    #Is the login mapped as a user? Logins already mapped in the database can not be the owner
                    elseif ($db.Users.name -contains $TargetLogin) {
                        Write-Message -Level Warning -Message "$dbname on $instance has $TargetLogin as a mapped user. Mapped users can not be database owners."
                    } else {
                        $db.SetOwner($TargetLogin)
                        [PSCustomObject]@{
                            ComputerName = $server.ComputerName
                            InstanceName = $server.ServiceName
                            SqlInstance  = $server.DomainInstanceName
                            Database     = $dbname
                            Owner        = $TargetLogin
                        }
                    }
                } catch {
                    Stop-Function -Message "Failure updating owner." -ErrorRecord $_ -Target $instance -Continue
                }
            }
        }
    }
}