loop through sql results and delete the single rows - c#

Im trying to delete persons from a list through a for loop. My problem is now that im trying to find each id to delete the specific row of my database but i dont know how i can do it with a for loop.
My Code right now:
[HttpPost("delUebertrag/")]
public async Task<ActionResult<ProzessPersonenzuordnungen>> delRecUebertrag([FromBody] recUebertragModel user)
{
ProzessPersonenzuordnungen ppz = new();
for (var i = 0; i <= user.personList.Length; i++)
{
Guid personId = new Guid(user.personList[i]);
ppz.ProzessId = new Guid(user.prozessId);
var prozessPersonenzuordnungen = _context.ProzessPersonenzuordnungens.Where(p => p.ProzessId == ppz.ProzessId && p.PersonId == personId);
if (prozessPersonenzuordnungen == null)
{
return NotFound();
}
//Everythings works fine above, prozessPersonenzuordnungen haves for Example 2 results
for(var j = 0; j < prozessPersonenzuordnungen.Count(); j++) // i dont know if Counts is fine, looking for something like length of the results
{
var toDeletingRow = await _context.ProzessPersonenzuordnungens.FindAsync(prozessPersonenzuordnungen.Select(p => p.ProzessPersonenzuordnungId)); // Here i need to go through every singleId of my results, something like p.ProzessPersonenzuordnungId[j](does not work)
_context.ProzessPersonenzuordnungens.Remove(toDeletingRow);
await _context.SaveChangesAsync();
}
}
return Ok();
}


The FindAsync can be only used for single item. Instead do
var rowsToDelete = _context.ProzessPersonenzuordnungens.Where(x=> prozessPersonenzuordnungen.Select(p => p.ProzessPersonenzuordnungId).Contains(x.Id));
And instead of Remove, use
_context.ProzessPersonenzuordnungens.RemoveRange(rowsToDelete);
And one important thing, accessing database in a loop is a very bad practice.
Try to do it without the loop.
Edit:
Try this
ProzessPersonenzuordnungen ppz = new ProzessPersonenzuordnungen();
for (var i = 0; i <= user.personList.Length; i++)
{
Guid personId = new Guid(user.personList[i]);
ppz.ProzessId = new Guid(user.prozessId);
var prozessPersonenzuordnungen = _context.ProzessPersonenzuordnungens.Where(p => p.ProzessId == ppz.ProzessId && p.PersonId == personId)
.Select((x)=> x.ProzessPersonenzuordnungId);
if (prozessPersonenzuordnungen == null)
{
return NotFound();
}
var rowsToDelete = _context.ProzessPersonenzuordnungens.Where(x => prozessPersonenzuordnungen.Contains(x.Id));
_context.ProzessPersonenzuordnungens.RemoveRange(rowsToDelete);
await _context.SaveChangesAsync();
return Ok();
}

Related

Entity Framework: Load data from different tables in one query

In my C# project with EF Core 5.0, I have several independents tables: Clothes, Hairs, Makeup. Some of their columns are similar, but some are not..`
I need to write a method that will load the rows from these tables. What I have now is:
public async Task<(ClothesDbModel[] clothes, MakeupDbModel[] makeups, HairDbModel[] hairs)> GetDressup(int[] clothesIds, int[] makeupIds, int[] hairIds)
{
ClothesDbModel[] clothes = new ClothesDbModel[0];
if (clothesIds.Length > 0)
{
clothes = await _dbContext.Clothes.Where(c => clothesIds.Contains(c.Id)).ToArrayAsync();
}
MakeupDbModel[] makeups = new MakeupDbModel[0];
if (makeupIds.Length > 0)
{
makeups = await _dbContext.Makeups.Where(c => makeupIds.Contains(c.Id)).ToArrayAsync();
}
HairDbModel[] hairs = new HairDbModel[0];
if (hairIds.Length > 0)
{
hairs = await _dbContext.Hairs.Where(c => hairIds.Contains(c.Id)).ToArrayAsync();
}
return (clothes, makeups, hairs);
}
However, in this case, I have 3 separate queries to the database (3 awaits). I believe that is not the best way to load the data from a performance point of view. Maybe I can load the same data using DbContext only once&

I hope it will work with EF. But I know there are problems with Concat, so it may fail.
class CombinedResult
{
public ClothesDbModel Clothes;
public MakeupDbModel Makeup;
public HairDbModel Hair;
}
...
public async Task<(ClothesDbModel[] clothes, MakeupDbModel[] makeups, HairDbModel[] hairs)> GetDressup(int[] clothesIds, int[] makeupIds, int[] hairIds)
{
var queries = new List<IQueryable<CombinedResult>>();
if (clothesIds.Length > 0)
{
queries.Add(_dbContext.Clothes.Where(c => clothesIds.Contains(c.Id)).Select(c => new CombinedResult { Clothes = c }));
}
if (makeupIds.Length > 0)
{
queries.Add(_dbContext.Makeups.Where(c => makeupIds.Contains(c.Id)).Select(c => new CombinedResult { Makeup = c }));
}
if (hairIds.Length > 0)
{
queries.Add(_dbContext.Hairs.Where(c => hairIds.Contains(c.Id)).Select(c => new CombinedResult { Hair = c }));
}
var clothes = new List<ClothesDbModel>();
var makeups = new List<MakeupDbModel>();
var hairs = new List<HairDbModel>();
if (queries.Count > 0)
{
var query = queries[0];
for (var i = 1; i < queries.Count; i++)
{
query = query.Concat(queries[i]);
}
var items = await query.ToListAsync();
foreach (var item in items)
{
if (item.Clothes != null)
clothes.Add(item.Clothes);
else if (item.Makeup != null)
makeups.Add(item.Makeup);
else if (item.Hair != null)
hairs.Add(item.Hair);
}
}
return (clothes.ToArray(), makeups.ToArray(), hairs.ToArray());
}

IEnumerable failed to set element

I have a ViewModel that contains different elements inside different tables that I tend to assign to it by query.
My problem is that I can't do this with IEnumerable (in GetAll() below), it keeps returning me null for RoomCode but for a single item (in GetDeviceId() below) then it works fine.
public IEnumerable<DeviceViewModel> GetAll()
{
var result = deviceRepository.GetAll().Select(x => x.ToViewModel<DeviceViewModel>());
for(int i = 0; i < result.Count(); i++)
{
int? deviceID = result.ElementAt(i).DeviceId;
result.ElementAt(i).RoomCode = deviceRepository.GetRoomCode(deviceID);
}
return result;
}
public DeviceViewModel GetDeviceID(int deviceID)
{
var result = new DeviceViewModel();
var device = deviceRepository.Find(deviceID);
if (device != null)
{
result = device.ToViewModel<DeviceViewModel>();
result.RoomCode = deviceRepository.GetRoomCode(deviceID);
}
else
{
throw new BaseException(ErrorMessages.DEVICE_LIST_EMPTY);
}
return result;
}
public string GetRoomCode(int? deviceID)
{
string roomCode;
var roomDevice = dbContext.Set<RoomDevice>().FirstOrDefault(x => x.DeviceId == deviceID && x.IsActive == true);
if (roomDevice != null)
{
var room = dbContext.Set<Room>().Find(roomDevice.RoomId);
roomCode = room.RoomCode;
}
else
{
roomCode = "";
}
return roomCode;
}

First, you need to materialize the query to a collection in local memory. Otherwise, the ElementAt(i) will query the db and give back some kind of temporary object each time it is used, discarding any change you do.
var result = deviceRepository.GetAll()
.Select(x => x.ToViewModel<DeviceViewModel>())
.ToList(); // this will materialize the query to a list in memory
// Now modifications of elements in the result IEnumerable will be persisted.
You can then go on with the rest of the code.
Second (and probably optional), I also recommend for clarity to use foreach to enumerate the elements. That's the C# idiomatic way to loop through an IEnumerable:
foreach (var element in result)
{
int? deviceID = element.DeviceId;
element.RoomCode = deviceRepository.GetRoomCode(deviceID);
}

Merging lists with a for loop

I'm working on an algorithm which can generate 2 types of recommendations, restaurants and dishes. All of this works fine, but I wanted to merge these 2 types of recommendations in a single list, which is where I encountered some issues. From my previous question I concluded that I needed a wrapper class, which I have set up like this:
public class RecommenderItem
{
public Guid Id { get; set; }
public object Entity { get; set; }
}
Now I want to alternate the 2 types of recommendations so the list would look like this:
[Restaurant][Dish][Restaurant][Dish][Restaurant][Dish] //Etc...
Note that these recommendations are completely separate. They are generated purely based on the user's preference, and they have no correlation in between them. My product owner wants to show these recommendations on the home page of our app like this.
These lists are different in length, so if I have added all items from a list, I wanted to just add the remaining objects from the other list. A possible scenario of this could look like this:
/*Other objects before this...*/[Dish][Restaurant][Dish][Dish][Dish] //Etc...
Here did the list of restaurant objects run out and I just wanted to add the remaining dish recommendations at the end of the list.
I have gotten this far, but I'm unsure how I would catch an IndexOutOfBounds exception and add the rest of the remaining objects at the end.
public List<RecommenderItem> GetMergedRecommendationLists(List<Restaurant> restaurantRecommendations,
List<Dish> dishRecommendations)
{
//Setting up the output list.
List<RecommenderItem> output = new List<RecommenderItem>();
int count = 0;
//Check which list is longer and use that count
if (restaurantRecommendations.Count > dishRecommendations.Count)
count = dishRecommendations.Count;
else
count = restaurantRecommendations.Count;
for (int i = 0; i < count; i++)
{
//I'm fully aware this isn't the most optimal way of doing this,
//but I'm only looking at functionality here, optimizing performance comes later.
var restRecommendation = restaurantRecommendations[i];
var dishRecommendation = dishRecommendations[i];
output.Add(new RecommenderItem()
{
Id = restRecommendation.Id,
Entity = restRecommendation
});
output.Add(new RecommenderItem()
{
Id = dishRecommendation.Id,
Entity = dishRecommendation
});
}
return output;
}
Does anyone have an idea how I could do this? Could I just catch an IndexOutOfBounds exception and use .AddRange() for the remaining objects? I'm not sure how I could check which list was out of bounds.
Let me know if I should elaborate more and thanks in advance!
Edit: -removed because it wasn't fair.-

This is a fairly succinct way of doing this.
While not Linq, it works in the spirit of the way Linq works by deferring doing any work until the resulting sequence is enumerated:
public static IEnumerable<RecommenderItem> Merge(IEnumerable<Restaurant> restaurants, IEnumerable<Dish> dishes)
{
using (var r = restaurants.GetEnumerator())
using (var d = dishes.GetEnumerator())
{
while (true)
{
bool rAvailable = r.MoveNext();
bool dAvailable = d.MoveNext();
if (rAvailable)
yield return new RecommenderItem { Id = r.Current.Id, Entity = r.Current };
if (dAvailable)
yield return new RecommenderItem { Id = d.Current.Id, Entity = d.Current };
if (!rAvailable && !dAvailable)
break;
}
}
}
If you happen to be using the MoreLinq NuGet package that includes the ZipLongest extension method, you can use the following simplified implementation instead:
public static IEnumerable<RecommenderItem> Merge(IEnumerable<Restaurant> restaurants, IEnumerable<Dish> dishes)
{
foreach (var item in restaurants.ZipLongest(dishes, (r, d) => new { r, d }))
{
if (item.r != null)
yield return new RecommenderItem { Id = item.r.Id, Entity = item.r };
if (item.d != null)
yield return new RecommenderItem { Id = item.d.Id, Entity = item.d };
}
}
Addendum
As #InBetween posted in his answer, you can put the interleaving logic into an extension method. Here's my version; it's substantially the same, except I've added a small optimisation to avoid calling .MoveNext() when its not necessary:
public static class EnumerableExt
{
public static IEnumerable<T> Interleave<T>(this IEnumerable<T> a, IEnumerable<T> b)
{
using (var ae = a.GetEnumerator())
using (var be = b.GetEnumerator())
{
bool aAvailable = true;
bool bAvailable = true;
while (aAvailable || bAvailable)
{
aAvailable = aAvailable && ae.MoveNext();
bAvailable = bAvailable && be.MoveNext();
if (aAvailable)
yield return ae.Current;
if (bAvailable)
yield return be.Current;
}
}
}
}
Once you have that, I realised that you don't need to write an implict operator. Instead, you can just convert the two sequences to the resultant type before calling Interleave() like so:
var restaurantsAsRecommenderItems =
restaurantRecommendations
.Select(r => new RecommenderItem {Id = r.Id, Entity = r});
var dishesAsRecommenderItems =
dishRecommendations
.Select(d => new RecommenderItem {Id = d.Id, Entity = d});
var result =
restaurantsAsRecommenderItems
.Interleave(dishesAsRecommenderItems)
.ToList();

My recommendation would be to just make simple implicit operator :
public static implicit operator RecommenderItem(Restaurant restaurant) {
return new RecommenderItem { Id = restaurant.Id, Entity = restaurant };
}
Then you have possibility to convert these types easily like :
Restaurant rest = //...
RecommenderItem rItem = rest; // here the implicit operator is called
After doing this you can just use one for loop :
int count = Math.Max(restaurantRecommendations.Count, dishRecommendations.Count);
for ( int i = 0; i < count; i++ ) {
if ( i < restRecommendations.Count )
output.Add(restRecommendations[i]);
if ( i < dishRecommendations.Count )
output.Add(dishRecommendations[i]);
}
This will make your work much more easier.

Well, there are probably more elegant LINQ solutions but you have already most, it's also a very efficient approach:
public List<RecommenderItem> GetMergedRecommendationLists(List<Restaurant> restaurantRecommendations, List<Dish> dishRecommendations)
{
//Setting up the output list.
List<RecommenderItem> output = new List<RecommenderItem>();
int count = Math.Min(restaurantRecommendations.Count, dishRecommendations.Count);
for (int i = 0; i < count; i++)
{
var restRecommendation = restaurantRecommendations[i];
var dishRecommendation = dishRecommendations[i];
output.Add(new RecommenderItem()
{
Id = restRecommendation.Id,
Entity = restRecommendation
});
output.Add(new RecommenderItem()
{
Id = dishRecommendation.Id,
Entity = dishRecommendation
});
}
int remainingRestaurant = restaurantRecommendations.Count - count;
int remainingDishes = dishRecommendations.Count - count;
if (remainingRestaurant > 0)
{
for (int i = count; i < restaurantRecommendations.Count; i++)
{
var restRecommendation = restaurantRecommendations[i];
output.Add(new RecommenderItem()
{
Id = restRecommendation.Id,
Entity = restRecommendation
});
}
}
else if (remainingDishes > 0)
{
for (int i = count; i < dishRecommendations.Count; i++)
{
var dishRecommendation = dishRecommendations[i];
output.Add(new RecommenderItem()
{
Id = dishRecommendation.Id,
Entity = dishRecommendation
});
}
}
return output;
}

A simple way of doing it would be:
public static IEnumerable<T> Merge<T>(this IEnumerable<T> first, IEnumerable<T> second)
{
using (var firstEnumerator = first.GetEnumerator())
using (var secondEnumerator = second.GetEnumerator())
{
while (firstEnumerator.MoveNext())
{
yield return firstEnumerator.Current;
if (secondEnumerator.MoveNext())
{
yield return secondEnumerator.Current;
}
}
while (secondEnumerator.MoveNext())
{
yield return secondEnumerator.Current;
}
}
}

After having created two arrays of restaurants and dishes of the same type RecommenderItem, you can use the Zip method like :
var restaurants = restaurantRecommendations.Select(x => new RecommenderItem {
Id = x.Id,
Entity = x
}).ToArray();
var dishes = dishRecommendations.Select(x => new RecommenderItem {
Id = x.Id,
Entity = x
}).ToArray();
var output = restaurants.Zip(dishes, (r, d) => new[] { r, d })
.SelectMany(r => r).Concat(dishes.Skip(restaurants.Length))
.Concat(restaurants.Skip(dishes.Length));

Restaraunt and Dish would have to share a base type:
restaurantRecommendations.Select(item => new RecommenderItem()
{
Id = item.Id,
Entity = item
});
dishRecommendations.Select(item => new RecommenderItem()
{
Id = item.Id,
Entity = item
});
Once that's the case you could use something like this slightly modified version of Zip (from System.Linq):
private static IEnumerable<T> ZipThrough<T>(IEnumerable<T> first, IEnumerable<T> second)
{
if (first == null) throw new ArgumentNullException(nameof(first));
if (second == null) throw new ArgumentNullException(nameof(second));
using (var e1 = first.GetEnumerator())
{
using (var e2 = second.GetEnumerator())
{
while (true)
if (e1.MoveNext())
{
yield return e1.Current;
if (e2.MoveNext()) yield return e2.Current;
}
else if (e2.MoveNext())
{
yield return e2.Current;
}
else
{
break;
}
}
}
}

MVCCrud Using LinqToEntities

There is a sample application called MVCCrud. This example is quite good and I would like to use it as the framework on a project that I am working on.
The problem is that MVCCrud uses LingToSQL and I would like to use LinqToEntities. I got most everything to work correctly once I converted over to LinqToEntities except one place.
In the following code on the lines i = typeof(TModel).GetProperty(primaryKey).GetValue(p, null),
cell = getCells(p)
it gives a Linq to Entities does not recognize GetValue.
Can someone help me refactor the following code?
items = items.OrderBy(string.Format("{0} {1}", sidx, sord)).Skip(pageIndex * pageSize).Take(pageSize).AsQueryable();
// Generate JSON
var jsonData =
new
{
total = totalPages,
page,
records = totalRecords,
rows = items.Select(
p => new
{
// id column from repository
i = typeof(TModel).GetProperty(primaryKey).GetValue(p, null),
cell = getCells(p)
}).ToArray()
};
return Json(jsonData);
and here is the getCell method:
private string[] getCells(TModel p)
{
List<string> result = new List<string>();
string a = actionCell(p);
if (a != null)
{
result.Add(a);
}
foreach (string column in data_rows.Select(r => r.value))
{
try
{
// hack for tblcategory.name
string[] parts = column.Split('.');
// Set first part
PropertyInfo c = typeof(TModel).GetProperty(parts[0]);
object tmp = c.GetValue(p, null);
// loop through if there is more than one depth to the . eg tblCategory.name
for (int j = 1; j < parts.Length; j++)
{
c = tmp.GetType().GetProperty(parts[j]);
tmp = c.GetValue(tmp, null);
}
if (tmp.GetType() == typeof(DateTime))
{
result.Add(((DateTime)tmp).ToString(dateTimeFormat));
}
else if (tmp.GetType() == typeof(float))
{
result.Add(((float)tmp).ToString(decimalFormat));
}
else if (tmp.GetType() == typeof(double))
{
result.Add(((double)tmp).ToString(decimalFormat));
}
else if (tmp.GetType() == typeof(decimal))
{
result.Add(((decimal)tmp).ToString(decimalFormat));
}
else
{
result.Add(tmp.ToString());
}
}
catch (Exception)
{
result.Add(string.Empty);
}
}
return result.ToArray();
}

Do this ToList() instead of AsQueryable():
items = items.OrderBy(string.Format("{0} {1}", sidx, sord)).Skip(pageIndex * pageSize).Take(pageSize).ToList();
You can't execute any external method "within" linq query.
And may you say that was working in Linq2Sql then you should know when you call any external method "Like ToString()" Linq2Sql will fetch all data from database then handle your query in the memory and that maybe a serious harming if you have a lot of records.
For more information look at this

Entity Random Select from DB C# MVC

Try to find the solution but i cant.
So problem is next one. I have the EDM model of database. I have a class with functions to get data from DB.
Like this:
public IQueryable<photos> FindUserPhotos(string userlogin)
{
return from m in db.photos
where m.userlogin == userlogin
select m;
}
How to get the Random 10 lines from DB?

I always use this method for get custom entity OrderBy(x => Guid.NewGuid())
public photos Find10RandomUserPhotos(string userlogin)
{
return db.photos.Where(x => x.userlogin == userlogin).OrderBy(x => Guid.NewGuid()).Take(10).ToList();
}

Following Random row from Linq to Sql
public photos FindRandomUserPhoto(string userlogin)
{
var qry = FindUserPhotos(userlogin);
int count = qry.Count();
int index = new Random().Next(count);
return qry.Skip(index).FirstOrDefault();
}
public Array<photos> Find10RandomUserPhotos(string userlogin)
{
var result = New Array<photos>;
for (i = 0; i < 10; i++) {
result.add(FindRandomUserPhoto(userlogin));
}
return result
}

Categories