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var ListeLandstriche = from LS in Daten.Landstriche
                       where (LS.LandID1 == 2 || LS.LandID2 == 2)
                       orderby LS.Landstrich
                       select new { LS.Landstrich };					

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var landstriche = context.Landstriche.Include("Land1")
                                     .Include("Land2")
                                     .Include("Land3")
                                     .Include("Land4")
                                     .Include("Land5")
                                     .Include("Land6").ToList();					

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var laender = context.Laender.ToArray();
var landstriche = context.Landstriche.ToList();					

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var ListeLandstriche5 = from LS15 in Landstriche5.Regionen
                                                  where (LS15.RegionID == ((int)((DataRowView)regionenBindingSource.List[Auswahl_Region1.SelectedIndex])["RegionID"]) || LS15.RegionID == 99999)
                                                  from LS25 in LS15.Länder
                                                  where LS25.RegionID == LS15.RegionID
                                                  from LS45 in LS25.Landstriche
                                                  //from LS46 in LS25.Landstriche1
                                                  //from LS47 in LS25.Landstriche2
                                                  where (LS45.LandID1 == LS25.LandID)
                                                  //where (LS46.LandID2 == LS25.LandID)
                                                  //where (LS47.LandID3 == LS25.LandID)
                                                  orderby (LS45.Landstrich)
                                                  select new { LS45.Landstrich };					

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DataSet1 ds = new DataSet1();
RegionenTableAdapter regionenTableAdapter = new RegionenTableAdapter();
regionenTableAdapter.Fill(ds.Regionen);
LänderTableAdapter länderTableAdapter = new LänderTableAdapter();
länderTableAdapter.Fill(ds.Länder);
LandstricheTableAdapter landstricheTableAdapter = new LandstricheTableAdapter();
landstricheTableAdapter.Fill(ds.Landstriche);
regionenBindingSource.DataSource = ds.Regionen;					

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var länderLandstrichCollection = ds.Länder.Where(l => l.RegionId == ((int)((DataRowView)regionenBindingSource.List[comboBox1.SelectedIndex])["RegionId"]) || l.RegionId == 9999)
                .Select(l=> l.GetLandstricheRowsByFK_Landstriche_Länder()
                  .Union(l.GetLandstricheRowsByFK_Landstriche_Länder1()
                  .Union(l.GetLandstricheRowsByFK_Landstriche_Länder2()
                  .Union(l.GetLandstricheRowsByFK_Landstriche_Länder3()
                  .Union(l.GetLandstricheRowsByFK_Landstriche_Länder4()
                  .Union(l.GetLandstricheRowsByFK_Landstriche_Länder5()
                  .Union(l.GetLandstricheRowsByFK_Landstriche_Länder6()
                  .Union(l.GetLandstricheRowsByFK_Landstriche_Länder7()))))))));

foreach (var land in länderLandstrichCollection)
{
  foreach (DataSet1.LandstricheRow landstrich in land)
  {
  
  }
}					

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foreach (var land in länderLandstrichCollection)
{
  foreach (IEnumerable<DataSet1.LandstricheRow> landstrichInLand in länderLandstrichCollection)
  {
    List<DataSet1.LandstricheRow> landstricheInLaenderList = landstrichInLand.ToList();
    }   
}					

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RegionenTableAdapter regionenTableAdapter = new RegionenTableAdapter();
regionenTableAdapter.Fill(ds.Regionen);
LänderTableAdapter länderTableAdapter = new LänderTableAdapter();
länderTableAdapter.Fill(ds.Länder);
LandstricheTableAdapter landstricheTableAdapter = new LandstricheTableAdapter();
landstricheTableAdapter.Fill(ds.Landstriche);
LandLandstricheTableAdapter landLandstricheTableAdapter = new LandLandstricheTableAdapter();
landLandstricheTableAdapter.Fill(ds.LandLandstriche);					

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EnumerableRowCollection<DataSet1.LänderRow> länder = ds.Länder.Where(l => l.RegionId == ((int)((DataRowView)regionenBindingSource.List[0])["RegionId"]) || l.RegionId == 9999);
foreach (DataSet1.LänderRow land in länder)
{
  DataSet1.LandLandstricheRow[] landLandstriche = land.GetLandLandstricheRows();
}					

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foreach (DataSet1.LandstricheRow landstrich in landstricheInLaenderList)
{
   //landstrich ist also ein Landstrich in der Liste der Landstriche zu einem bestimmten Land   
}					

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DataSet1.LandstricheRow landstrich = landstricheInLaenderList.ElementAtOrDefault(0);
if (landstrich != null)
{
   //der übergebene Index wurde in der Liste gefunden    
}
else
{ 
   //der übergebene Index war nicht in der List, also ist landstrich null
}					

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List<DataSet1.LandstricheRow> gefilterteLandstriche = 
      landstricheInLaenderList.Where(l => l.LandstrichName.Equals("Landstrich1")).ToList();					

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EnumerableRowCollection<DataSet1.LänderRow> länder = ds.Länder.Where(l => l.RegionId == 
                      ((int)((DataRowView)regionenBindingSource.List[0])["RegionId"]) || l.RegionId == 9999);
foreach (DataSet1.LänderRow land in länder)
{
  DataSet1.LandLandstricheRow[] landLandstriche = land.GetLandLandstricheRows();
}					

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foreach (DataSet.LänderRow land in dataSet.Länder.Where(l => l.RegionId == 0 || l.RegionId == 9999))
{
  //erstmal eine Abfrage aller LandLandstriche in dem Land
  DataSet.LandLandstricheRow[] landLandstriche = land.GetLandLandstricheRows();
  //Abfrage aller Landstriche, dessen LandstrichId sich in dem Array befinden (also LandLandstrich.LandstrichId)  
  List<DataSet.LandstricheRow> landstricheImLand = dataSet.Landstriche.Where(ls => landLandstriche.Where
                            (lls => lls.LandstrichId == ls.LandstrichId).Count() > 0).ToList();
}					

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foreach (DataSet.LandLandstricheRow landLandstrich in landLandstriche)
  Console.WriteLine(string.Format("LandId: {0}, LandstrichId: {1}", landLandstrich.LandId, landLandstrich.LandstrichId));					

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foreach (DataSet.LandstricheRow landstrich in landstriche)
  Console.WriteLine(string.Format("LandstrichId: {0}, Landstrichname:{1}", landstrich.LandstrichId, landstrich.LandstrichName));