Using anonymous types - how to avoid lot of code

Question

I have this situation:

if (condition){
   var variable = (from el in ....) //linq to sql query
 }
else{
   var variable = (from el in ....) //linq to sql query
 }

// code where i can`t use the variable

I want to avoid copying code in both conditions.

var getHistoryTips = (from el in objDC.tickets
                      where el.typeOfGame == cANDu[0]
                      && el.username == Membership.GetUser(cANDu[1]).ProviderUserKey.ToString()
                      select new { el.AllGamesTickets, el.WGamesTickets}).FirstOrDefault();


var getHistoryTips = (from el in objDC.tickets
                      where el.typeOfGame == cANDu[0]
                      && el.results != null
                      && el.username == Membership.GetUser(cANDu[1]).ProviderUserKey.ToString()
                      select new { el.AllGamesTickets, el.WGamesTickets}).FirstOrDefault();

what do you want to avoid copying? Edit: Now I see your queries. They look identical. If the result of your conditions are the same, why do you even need the conditions? — user195488
– user195488, Commented Jul 6, 2011 at 18:16
I want to avoid to put "code" in if and else, only to have query. — gormit
– gormit, Commented Jul 6, 2011 at 18:20

Jon Skeet · Accepted Answer · 2011-07-06 18:20:27Z

8

Three options:

Firstly, you can use an "example" - to type the variable:

// Same anonymous type properties and types as later:
var variable = Enumerable.Repeat(0, new { ... });

if (condition) {
    variable = ...;
} else {
    variable = ...;
}

Alternatively, you could use the conditional operator:

var variable = condition ? ... first query ...
                         : ... second query ...

Thirdly, you could build the query up using composition instead. For example, if the only difference is the ordering, you could do:

var firstPart = ...;

var secondPart = condition ? query.OrderBy(...) : query.OrderByDescending(...);

var query = secondPart.Select(...);

EDIT: Now you've given an example, we can make this concrete:

string username = membership.GetUser(cANDu[1]).ProviderUserKey.ToString();
var query = objDC.tickets
                 .Where(el => el.typeOfGame == cANDu[0] &&
                              el.username == username);

if (condition)
{
    query = query.Where(el => el.results != null);
}

var result = query.Select(el => new { el.AllGamesTickets, el.WGamesTickets})
                  .FirstOrDefault();

answered Jul 6, 2011 at 18:20

Jon Skeet

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6 Comments

user195488 Over a year ago

See his latest comment: "want to avoid to put "code" in if and else, only to have query"

Jon Skeet Over a year ago

@0A0D: That's what my third option gives, and I now have a concrete example.

gormit Over a year ago

@Jon Skeet Any possibility to do this with two different tables in queries?

gormit Over a year ago

@Jon Skeet if I use conditional operator and in one query objDC.tickets, in second other table, then I have problem "no implicit convertion between System.Linq.IQueryable<ticket> and..."

Jon Skeet Over a year ago

@gormit: I suggest you ask in more detail in a new question.

|

Dirk · Accepted Answer · 2011-07-06 18:24:53Z

2

You might be able to use the ternary operator:

var variable = (condition) ? (from el in...) : (from el in...);

Where the first linq-to-sql statement (before the colon) is the true case and the linq-to-sql after the colon is the false case. So your code might look like:

var getHistoryTips = (condition) ? (from el in objDC.tickets
                                     where el.typeOfGame == cANDu[0]
                                     && el.username == Membership.GetUser(cANDu[1]).ProviderUserKey.ToString()
                                     select new { el.AllGamesTickets, el.WGamesTickets}).FirstOrDefault() : 
                                   (from el in objDC.tickets
                                     where el.typeOfGame == cANDu[0]
                                     && el.results != null
                                     && el.username == Membership.GetUser(cANDu[1]).ProviderUserKey.ToString()
                                     select new { el.AllGamesTickets, el.WGamesTickets}).FirstOrDefault();

edited Jul 6, 2011 at 18:24

answered Jul 6, 2011 at 18:20

Dirk

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1 Comment

user195488 Over a year ago

I think he wants to prevent typing it twice (e.g. concatenate queries adding in the extra conditional of el.results != null)

SaravananArumugam · Accepted Answer · 2011-07-06 18:24:14Z

1

Use your condition in the query itself in the where clause.

You may have to write something like,

var variable = (from el in .... where (condition && trueBlockCondition) || (!condition && falseBlockCondition)

answered Jul 6, 2011 at 18:24

SaravananArumugam

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Comments

Valera Kolupaev · Accepted Answer · 2011-07-06 18:37:00Z

Functionality you are asking for can be implemented using extensions method, instead of LINQ syntax.

Here are the example:

var source = objDC.tickets.Where(el => 
    el.typeOfGame == cANDu[0]
    && el.username == Membership.GetUser(cANDu[1]).ProviderUserKey.ToString());

if(condition)
    source = source.Where(el => el.results != null);

var getHistoryTips = source
    .Select(el => new { el.AllGamesTickets, el.WGamesTickets}))
    .FirstOrDefault();

If query getting complicated, as an option, selector can be implemented via Expression feature.

Expression<Func<ObjDCType, ShallowObjDCType>> selector = 
   (el) => new ShallowObjDC{ el.AllGamesTickets, el.WGamesTickets});

var getHistoryTips = source.Select(selector).FirstOrDefault();

This technique will allow you yo pass selector inside other function, in case things are getting more complex, however it requires you to define additional class or use dynamic, instead of anonymous classes.

Note, that you can't use Func without Expression, since this will cause ORM (LINQ/EF) to pull all object from database.

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