c# - How to fetch a model's relationship in a dynamic way? -

so have application makes use of sqlite database. have methods fetching models out of database. have repository communicaties database. , looks this:

public class photorepository     {          appdatabase db = null;          public photorepository ()         {             db = new appdatabase (constants.databasefilepath);         }          public photo getphoto(int id)         {             return db.getitem<photo>(id);         }          public ienumerable<photo> getphotos (int album_id)         {             return db.getitems<photo>().where( x => x.album_id == album_id );         }          public int savephoto (photo item)         {             return db.saveitem<photo>(item);         }          public int deletephoto(int id)         {             return db.deleteitem<photo>(id);         }      } 

i concerned getphotos(int album_id) method, because method approaches in database class looks following:

public ienumerable<t> getitems<t> () t : bl.contracts.ibusinessentity, new ()         {             lock (locker) {                 return (from in table<t> () select i).tolist ();             }         } 

as can see, retrieves of photo models database , after i'm, filtering out corresponds right album_id.

no question is:

how can rewrite method fetches out models corresponding album_id. or better, how can rewrite method filter relationship on property?

so managed solve own answer. maybe people interested in result, here comes.

i read post dynamic linq queries. post talking can found here. first thing did making filter class looks this:

public class filter     {          public enum op          {             equals,             greaterthan,             lessthan,             greaterthanorequal,             lessthanorequal,             contains,             startswith,             endswith         }          public string propertyname { ; set ; }         public op operation { ; set ; }         public object value { ; set ; }     } 

then made expressionbuilder class looks following:

public static class expressionbuilder  {     private static methodinfo containsmethod = typeof(string).getmethod("contains" );     private static methodinfo startswithmethod =          typeof(string).getmethod("startswith", new type [] {typeof(string)});     private static methodinfo endswithmethod =          typeof(string).getmethod("endswith", new type [] { typeof(string)});       public static expression<func<t,      bool >> getexpression<t>(ilist<filter> filters)     {                     if  (filters.count == 0)             return null ;          parameterexpression param = expression.parameter(typeof (t), "t" );         expression exp = null ;          if  (filters.count == 1)             exp = getexpression<t>(param, filters[0]);         else  if  (filters.count == 2)             exp = getexpression<t>(param, filters[0], filters[1]);         else          {             while  (filters.count > 0)             {                 var  f1 = filters[0];                 var  f2 = filters[1];                  if  (exp == null )                     exp = getexpression<t>(param, filters[0], filters[1]);                 else                      exp = expression.andalso(exp, getexpression<t>(param, filters[0], filters[1]));                  filters.remove(f1);                 filters.remove(f2);                  if  (filters.count == 1)                 {                     exp = expression .andalso(exp, getexpression<t>(param, filters[0]));                     filters.removeat(0);                 }             }         }          return expression.lambda<func<t, bool>>(exp, param);     }      private static expression getexpression<t>(parameterexpression param, filter filter)     {         memberexpression member = expression.property(param, filter.propertyname);         constantexpression constant = expression.constant(filter.value);          switch (filter.operation)         {         case  photowapp.dl.filter.op.equals:             return expression.equal(member, constant);          case  photowapp.dl.filter.op.greaterthan:             return expression.greaterthan(member, constant);          case photowapp.dl.filter.op.greaterthanorequal:             return expression.greaterthanorequal(member, constant);          case photowapp.dl.filter.op.lessthan:             return expression.lessthan(member, constant);          case photowapp.dl.filter.op.lessthanorequal:             return expression.lessthanorequal(member, constant);          case photowapp.dl.filter.op.contains:             return expression.call(member, containsmethod, constant);          case photowapp.dl.filter.op.startswith:             return expression.call(member, startswithmethod, constant);          case photowapp.dl.filter.op.endswith:             return expression.call(member, endswithmethod, constant);         }          return null ;     }      private static binaryexpression getexpression<t>     (parameterexpression param, filter filter1, filter  filter2)     {         expression bin1 = getexpression<t>(param, filter1);         expression bin2 = getexpression<t>(param, filter2);          return  expression.andalso(bin1, bin2);     } } 

then added method getitems<t>(list<filter> filters) looks following:

public ienumerable<t> getitems<t> (list<filter> filters) t : bl.contracts.ibusinessentity, new ()     {         lock (locker) {             var deleg = expressionbuilder.getexpression<t> (filters).compile ();             return (from in table<t>().where(deleg) select i).tolist();         }     } 

and retrieve records need, used following code.

public ienumerable<photo> getphotos (int album_id)     {         list<filter> filters = new list<filter> () {              new filter{                 propertyname = "album_id",                 operation = filter.op.equals,                 value = album_id             }         };         return db.getitems<photo>(filters);     } 

now can filter nicely on properties need! nice part solution can use class , property filter on.

i hope useful somebody!