c# - Where/when to populate lookup values? -

-

i've tried googling 2 days can't seem find answer.

i'd category class provide description based on id entered , return error if id not valid. best approach?

public class category {     private int _id;     private string _desc;      public category(int id)     {         id = id;     }      public int id      {                  {             return _id;         }          set          {             _id = value;              //_desc = value data access layer or throw error if id invalid                        }     }      public string description      {                  {             return _desc;         }            } }  public class person {     public int id {get; set;}      public category category {get; set;} }  public class myapp {     static void main()     {         person p = new person();          category c = new category(2);          p.category = c;     } }

since there potentially several instances of class category, waste memory-wise include values in class itself. instead should accessed elsewhere. instance static function in class.

public class categoryhelper {     public static string getcategorydesc(int catgeoryid)     {         ...access database description     } }

which use in description getter in category class:

public string description  {          {         return categoryhelper.getcategorydesc(this.id);     }        }

now, since have getcategorydesc in separate class can optimize performance. instance, if values lookup won't change duration of run can cache descriptions in memory avoid db trips. in following code call db first time call made , the results cached. called "memoization".

public class categoryhelper {     dictionary<int,string> cacheddesc; //dictionary used store descriptions     public static string getcategorydesc(int catgeoryid)     {         if (cacheddesc==null) cacheddesc = new dictionary<int,string>(); // instatiate dictionary first time         if(cacheddesc.containskey(catgeoryid)) //we check see if have cached value before         {             return cacheddesc[catgeoryid];         }         else         {             var description = .... value db             cacheddesc.add(catgeoryid, description); //store value later use             return description;         }     } }

you can make simpler , more complex, , since isolated in own function have little no changes elsewhere.


Comments

Post a Comment

Popular posts from this blog

c# - How Configure Devart dotConnect for SQLite Code First? -

-
can configure following sample code ? when run following code, error : no entity framework provider found ado.net provider invariant name 'devart.data.sqlite' setting in machine.config <system.data> <dbproviderfactories> <add name="dotconnect sqlite" invariant="devart.data.sqlite" description="devart dotconnect sqlite" type="devart.data.sqlite.sqliteproviderfactory, devart.data.sqlite, version=4.6.287.0, culture=neutral, publickeytoken=09af7300eec23701" /> </dbproviderfactories> </system.data> after add below block code in app.config <?xml version="1.0"?> <configuration>   <configsections> <!-- more information on entity framework configuration, visit http://go.microsoft.com/fwlink/?linkid=237468 --> <section name="entityframework" type="system.data.entity.internal.configfile.entityframeworksection, entit...
Read more

java - Copying object fields -

-
what best way of copying classes when need have 2 independent variables? have simple class: public class myclass { boolean = false; string b= "not empty"; } do need make method : assign(myclass data ) { a= data.a; b= data.b; } is there automatic method copy (duplicate) objects in java? do need make method : pretty close. instead of making method, should make constructor. such constructors called copy constructor , , create them this: myclass(myclass data) { = data.a; b = data.b; } and create copy of instance, use constructor this: myclass obj1 = new myclass(); myclass obj2 = new myclass(obj1); copy constructor can tedious : using copy constructor create deep-copy can tedious, when class has mutable fields. in case, assignment create copy of reference, , not object itself. have create copy of fields (if want deep copy). can go recursive. a better way create deep copy serialize , deserialize object. why not use clone()? ...
Read more

c++ - Clear the memory after returning a vector in a function -

-
i have function processes , stores lot of data in , returns results vector of class. amount of data stored in function tremendous , want clear storage memory of function after finished job. necessary (does function automatically clear memory) or should clear memory function? update: vector<customers> process(char* const *filename, vector<int> id) { vector<customers> list_of_customers; (perform actions) return list_of_customers; } variables defined locally within function automatically released @ end of function scope. destructors objects called, should free memory allocated objects (if objects coded correctly). example of such object std::vector . anything you've allocated new must have corresponding delete release storage. try avoid doing own allocation , use raii instead, i.e. containers or smart pointers.
Read more