functions/Set-DbaDatabaseOwner.ps1

function Set-DbaDatabaseOwner
{
<#
.SYNOPSIS
Sets database owners with a desired login if databases do not match that owner.
 
.DESCRIPTION
This function will alter database ownershipt 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 fuction 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
 
.NOTES
Original Author: Michael Fal (@Mike_Fal), http://mikefal.net
 
dbatools PowerShell module (https://dbatools.io, clemaire@gmail.com)
Copyright (C) 2016 Chrissy LeMaire
 
This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
 
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
 
You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>.
 
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
 
.PARAMETER SqlServer
SQLServer name or SMO object representing the SQL Server to connect to. This can be a collection and recieve pipeline input
 
.PARAMETER SqlCredential
PSCredential object to connect under. If not specified, currend Windows login will be used.
 
.PARAMETER Datbases
List of databases to apply changes to. Will accept a comma separated list or a string array.
     
.PARAMETER Exclude
List of databases to exclude
 
.PARAMETER TargetLogin
Specific login that you wish to check for ownership. This defaults to 'sa' or the sysadmin name if sa was renamed.
 
.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.
 
.LINK
https://dbatools.io/Set-DbaDatabaseOwner
 
.EXAMPLE
Set-DbaDatabaseOwner -SqlServer localhost
 
Sets database owner to 'sa' on all databases where the owner does not match 'sa'.
 
.EXAMPLE
Set-DbaDatabaseOwner -SqlServer localhost -TargetLogin DOMAIN\account
 
To set the database owner to DOMAIN\account on all databases where the owner does not match DOMAIN\account. Note that TargetLogin must be a valid security principal that exists on the target server.
 
.EXAMPLE
Set-DbaDatabaseOwner -SqlServer sqlserver -Databases db1, db2
 
Sets database owner to 'sa' on the db1 and db2 databases if their current owner does not match 'sa'.
#>

    [CmdletBinding(SupportsShouldProcess = $true)]
    Param (
        [parameter(Mandatory = $true, ValueFromPipeline = $true)]
        [Alias("ServerInstance", "SqlInstance")]
        [object[]]$SqlServer,
        [object]$SqlCredential,
        [string]$TargetLogin
    )
    
    DynamicParam { if ($SqlServer) { return Get-ParamSqlDatabases -SqlServer $SqlServer[0] -SqlCredential $SqlCredential } }
    
    BEGIN
    {
        $databases = $psboundparameters.Databases
        $exclude = $psboundparameters.Exclude
    }
    
    PROCESS
    {
        foreach ($servername in $SqlServer)
        {
            
            #connect to the instance
            Write-Verbose "Connecting to $servername"
            $server = Connect-SqlServer $servername -SqlCredential $SqlCredential
            
            # dynamic sa name for orgs who have changed their sa name
            if ($psboundparameters.TargetLogin.length -eq 0)
            {
                $TargetLogin = ($server.logins | Where-Object { $_.id -eq 1 }).Name
            }
            
            #Validate login
            if (($server.Logins.Name) -notcontains $TargetLogin)
            {
                if ($sqlserver.count -eq 1)
                {
                    throw "Invalid login: $TargetLogin"
                }
                else
                {
                    Write-Warning "$TargetLogin is not a valid login on $servername. Moving on."
                    Continue
                }
            }
            
            #Get database list. If value for -Databases is passed, massage to make it a string array.
            #Otherwise, use all databases on the instance where owner not equal to -TargetLogin
            Write-Verbose "Gathering databases to update"
            
            #use where owner and target login do not match
            #exclude system dbs
            $dbs = $server.Databases | Where-Object {$_.Owner -ne $TargetLogin -and @('master', 'model', 'msdb', 'tempdb', 'distribution') -notcontains $_.Name}

            #filter collection based on -Databases/-Exclude parameters
            if ($Databases.Length -gt 0)
            {
                $dbs = $dbs | Where-Object { $databases -contains $_.Name }
            }
            
            if ($Exclude.Length -gt 0)
            {
                $dbs = $dbs | Where-Object { $Exclude -notcontains $_.Name }
            }
                        
            Write-Verbose "Updating $($dbs.Count) database(s)."
            foreach ($db in $dbs)
            {
                $dbname = $db.name
                If ($PSCmdlet.ShouldProcess($servername, "Setting database owner for $dbname to $TargetLogin"))
                {                    
                    try
                    {
                        Write-Output "Setting database owner for $dbname to $TargetLogin on $servername"
                        # Set database owner to $TargetLogin (default 'sa')
                        # Ownership validations checks
                        
                        #Database is online and accessible
                        if($db.Status -ne 'Normal'){
                            Write-Warning "$dbname on $servername 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 $false) {
                            Write-Warning "$dbname on $servername is not in an updateable state and can not be altered. It will be skipped."
                        } 
                        #Is the login mapped as a user? Logins already mapped in the database can not be the owner
                        elseif ($db.Users.name -contains $TargetLogin) {
                            Write-Warning "$dbname on $servername has $TargetLogin as a mapped user. Mapped users can not be database owners."
                        }
                        else {
                            $db.SetOwner($TargetLogin)
                        }
                    }
                    catch
                    {
                        # write-exception writes the full exception to file
                        Write-Exception $_
                        throw $_
                        Continue
                    }
                }
            }
        }
    }
    
    END
    {
        if ($dbs.count -eq 0)
        {
            Write-Output "Lookin' good! Nothing to do."
        }
        
        Write-Verbose "Closing connection"
        $server.ConnectionContext.Disconnect()
    }
}