SPAlert.Filter not working - sharepoint-2013

Question

Can anybody help with SPAlert filters on Sharepoint 2013?
If I set Filter property on SPAlert instance the alert has not been sent
SPAlert newAlert = user.Alerts.Add();
SPAlertTemplateCollection alertTemplates = new SPAlertTemplateCollection(
(SPWebService)(SPContext.Current.Site.WebApplication.Parent));
newAlert.AlertType = SPAlertType.List;
newAlert.List = list;
newAlert.Title = alertTitle;
newAlert.DeliveryChannels = SPAlertDeliveryChannels.Email;
newAlert.EventType = eventType;
newAlert.AlertFrequency = SPAlertFrequency.Immediate;
newAlert.AlertTemplate = alertTemplates[Constants.AlertTemplates.GenericListCustom];
var wsm = new WorkflowServicesManager(web);
var wss = wsm.GetWorkflowSubscriptionService();
var subscriptions = wss.EnumerateSubscriptionsByList(list.ID);
bool assotiationExist = false;
var guid = Constants.Workflows.ApprovalWF.Guid;
foreach (var subs in subscriptions)
{
assotiationExist = subs.DefinitionId == guid;
if (assotiationExist)
{
newAlert.Filter = "<Query><Eq><FieldRef Name=\"ApprovalStatus\"/><Value type=\"string\">Approved</Value></Eq></Query>";
}
}
newAlert.Update(false);

Answer 1

If I set Filter property on SPAlert instance the alert has not been sent
What do you need exactly ?
If you just want to change the filter (alert condition), did you simply try :
newAlert.AlertType = SPAlertType.List;
newAlert.List = list;
newAlert.Title = alertTitle;
newAlert.DeliveryChannels = SPAlertDeliveryChannels.Email;
newAlert.EventType = eventType;
newAlert.AlertFrequency = SPAlertFrequency.Immediate;
newAlert.AlertTemplate = alertTemplates[Constants.AlertTemplates.GenericListCustom];
newAlert.Filter = "<Query><Eq><FieldRef Name=\"ApprovalStatus/New\"/><Value type=\"string\">Approved</Value></Eq></Query>";
newAlert.Update(false);
I have just added a /New in your filter query. Query filter in alert need to get a /New or a /Old in your field.
If your alert still doesn't work, it might be something else than the filter.

Answer 2

The problem was in line newAlert.EventType = eventType. eventType was SPEventType.Add. That was the reason of not sending alert after Workflow set the ApprovalStatus field to «Approved».
I’ve modified algourithm. Now eventType is SPEventType.Modify and I added new field "IsNewAlertSent" to list. When event fires the first time then I send email and set the "IsNewAlertSent" field
Final code is shown below.
class UserAlertManager:
..
newAlert.EventType = (eventType == SPEventType.Add? SPEventType.Modify: eventType);
newAlert.AlertFrequency = SPAlertFrequency.Immediate;
newAlert.AlertTemplate = alertTemplates[Constants.AlertTemplates.GenericListCustom];
..
if (assotiationExist)
{
newAlert.Filter = "<Query><Eq><FieldRef name=\"ApprovalStatus\"/><Value type=\"Text\">Approved</Value></Eq></Query>";
newAlert.Properties.Add("grcustomalert", "1");
}
..
newAlert.Update(false);
class GRCustomAlertHandler:
...
string subject = string.Empty;
string body = string.Empty;
bool grCustomAlert = Utils.IsSPAlertCustom(ahp.a);
if (ahp.eventData[0].eventType == (int)SPEventType.Modify && grCustomAlert)
{
SPListItem item = list.GetItemById(ahp.eventData[0].itemId);
var isNewAlertSentField = item.Fields.GetFieldByInternalName(Constants.Fields.IsNewAlertSent);
if (isNewAlertSentField != null && (item[Constants.Fields.IsNewAlertSent] == null || !(bool)item[Constants.Fields.IsNewAlertSent]))
{
...
Utils.SendMail(web, new List<string> { ahp.headers["to"].ToString() }, subject, body);
item[Constants.Fields.IsNewAlertSent] = true;
using (new DisabledItemEventScope())
{
item.SystemUpdate(false);
}
}
}
...