Only Update Entity (Parent or children) if Property Values Have Changed with EF - entity-framework

Question

As I build a project with Entity Framework 6 (using EF for the first time), I noticed that when I only Update the relationships of an Entity, EF updates the main Entity too.
I can tell this is happening because I'm using System Versioned tables on Sql Server 2017.
This is a made up scenario, but most of the concept is here.
public async Task<ActionResult> Edit([Bind(Include="Id,Name,LocationTimes")] LocationViewModel locationVM) {
if (ModelState.IsValid) {
var location = await _db.Locations.FirstOrDefaultAsync(l => l.Id == locationsViewModel.Id && l.UserId == UserId);
if (location == null) {
return HttpNotFound();
}
location.Name = locationsViewModel.Name;
// ... other properties
foreach (var day in locationsViewModel.LocationTimes.Days) {
var time = new Time {
Day = day.Day,
OpenTime = day.OpenTime,
CloseTime = day.CloseTime,
};
// Find current Time or keep newly created
time = await time.FindByTimeAsync(time, _db) ?? time;
// Find LocationTime with same day
var locationTime = location.LocationTimes.FirstOrDefault(lt => lt.Time.Day == day.Day);
// If all times are the same, skip (continue)
if (locationTime != null && locationTime.Time.OpenTime == time.OpenTime && locationTime.Time.CloseTime == time.CloseTime)
continue;
if (locationTime != null && (locationTime.Time.OpenTime != time.OpenTime || locationTime.Time.CloseTime != time.CloseTime)) {
// Remove, At least one of the Times do not match
locationTime.Time = time;
_db.Entry(locationTime).State = EntityState.Modified;
} else {
location.LocationTimes.Add(new LocationTime {
Location = location,
Time = time,
});
}
}
_db.Entry(location).State = EntityState.Modified;
await _db.SaveChangesAsync();
return RedirectToAction("Index");
}
}
I assume, that by marking the entire Entity as Modified, EF will call the update statement.
How can I avoid an UPDATE to the parent Entity, if no properties have changed on the parent, but still Add/Update the child relationships?
I assume I have to check that each property has not changed and therefore I should not be setting location state to Modified, but how would I handle the newly added Times?
Update #1
So I tried what I mentioned and it works, but is this the correct way to do this?
public async Task<ActionResult> Edit([Bind(Include="Id,Name,LocationTimes")] LocationViewModel locationVM) {
if (ModelState.IsValid) {
var location = await _db.Locations.FirstOrDefaultAsync(l => l.Id == locationsViewModel.Id && l.UserId == UserId);
if (location == null) {
return HttpNotFound();
}
/*******************
This is new part
*******************/
if (
location.Name != locationsViewModel.Name
// || ... test other properties
) {
location.Name = locationsViewModel.Name;
// ... other properties
_db.Entry(location).State = EntityState.Modified;
} else {
_db.Entry(location).State = EntityState.Unchanged;
}
/*******************/
foreach (var day in locationsViewModel.LocationTimes.Days) {
var time = new Time {
Day = day.Day,
OpenTime = day.OpenTime,
CloseTime = day.CloseTime,
};
// Find current Time or keep newly created
time = await time.FindByTimeAsync(time, _db) ?? time;
// Find LocationTime with same day
var locationTime = location.LocationTimes.FirstOrDefault(lt => lt.Time.Day == day.Day);
// If all times are the same, skip (continue)
if (locationTime != null && locationTime.Time.OpenTime == time.OpenTime && locationTime.Time.CloseTime == time.CloseTime)
continue;
if (locationTime != null && (locationTime.Time.OpenTime != time.OpenTime || locationTime.Time.CloseTime != time.CloseTime)) {
// Remove, At least one of the Times do not match
locationTime.Time = time;
_db.Entry(locationTime).State = EntityState.Modified;
} else {
location.LocationTimes.Add(new LocationTime {
Location = location,
Time = time,
});
}
}
/* removed, added above */
//_db.Entry(location).State = EntityState.Modified;
await _db.SaveChangesAsync();
return RedirectToAction("Index");
}
}

Answer 1

So after trial and error, I guess I misunderstood how EF handles the EntityState. I though if a child was Modified, you had to set the parent as Modified as well.
Gladly, that's not the case and the code below works as desired.
public async Task<ActionResult> Edit([Bind(Include="Id,Name,LocationTimes")] LocationViewModel locationVM) {
if (ModelState.IsValid) {
var location = await _db.Locations.FirstOrDefaultAsync(l => l.Id == locationsViewModel.Id && l.UserId == UserId);
if (location == null) {
return HttpNotFound();
}
/*******************
This is new part
check if at least one property was changed
*******************/
if (
location.Name != locationsViewModel.Name
|| location.Ref != locationsViewModel.Ref
// || ... test other properties
) {
location.Name = locationsViewModel.Name;
location.Ref = locationsViewModel.Ref;
// ... other properties
// Tell EF that the Entity has been modified (probably not needed, but just in case)
_db.Entry(location).State = EntityState.Modified;
} else {
// Tell EF that the Entity has *NOT* been modified
_db.Entry(location).State = EntityState.Unchanged;
}
/*******************/
foreach (var day in locationsViewModel.LocationTimes.Days) {
var time = new Time {
Day = day.Day,
OpenTime = day.OpenTime,
CloseTime = day.CloseTime,
};
// Find current Time or keep newly created
time = await time.FindByTimeAsync(time, _db) ?? time;
// Find LocationTime with same day
var locationTime = location.LocationTimes.FirstOrDefault(lt => lt.Time.Day == day.Day);
// If all times are the same, skip (continue)
if (locationTime != null && locationTime.Time.OpenTime == time.OpenTime && locationTime.Time.CloseTime == time.CloseTime)
continue;
if (locationTime != null && (locationTime.Time.OpenTime != time.OpenTime || locationTime.Time.CloseTime != time.CloseTime)) {
// Remove, At least one of the Times do not match
locationTime.Time = time;
_db.Entry(locationTime).State = EntityState.Modified;
} else {
location.LocationTimes.Add(new LocationTime {
Location = location,
Time = time,
});
}
}
/* removed, added above */
//_db.Entry(location).State = EntityState.Modified;
await _db.SaveChangesAsync();
return RedirectToAction("Index");
}
}