help with linq query

Question

Hi, i am trying to get some data, but i dont know how can i do a if in linq, this is how i am trying to do

from so in db.Operations
where ((opType!= "0" ? so.Operation == int.Parse(opType) : false) 
    && (idState!=0 ? so.State == idState : false) 
    && (start != null ? so.StartDate == start : false) 
    && (end !=null ? so.EndDate == end : false))
select so

the optype is a Int, the idState is a Int, end is a datetime, start is a datime

what i am trying to do is, if those aren't null they add to the query function, so i can get all data together

for example: in c# code

if((opType!= "0")
 where (so.Operation == int.Parse(opType)
if(idState!=0)
 where (so.Operation == int.Parse(opType) && so.State == idState
.......

so if that isn't null, that sentence in that sql query (the TRUE part, i dont want to use the false part), add it to the where, so i can search all parameters that aren't null or 0

Answer 1

opType!= "0" ? so.Operation == int.Parse(opType) : false

you should not use so.operation == int.parse.... instead use so.operation = int.Parse(opType)

Answer 2

Well not sure what you want exactly but here is a try:

var query = db.Operations.AsQueryable();

if (opType != null && opType != "0")
    query = query.Where(x => x.Operation == int.Parse(opType);

if (idState != 0) 
    query = query.Where(x => x.State == idState);

if (start != null) // assuming that start is of type DateTime? otherwise use DateTime.MinValue
    query = query.Where(x => x.StartDate.Date == start); // maybe >= is more appropriate

if (end != null) // also DateTime? assumed
    query = query.Where(x => x.EndDate.Date == end); // maybe <= is more appropriate

var result = query.ToList(); // e.g. could also do an foreach, depending what you want to do

The trick in this approach is to build up the query successively. The query will not be enumerated until .ToList() or foreach is used to enumerate the list.

Actually this should yield the same:

from so in db.Operations
where ((opType != null && opType!= "0" ? so.Operation == int.Parse(opType) : true) 
    && (idState!=0 ? so.State == idState : true) 
    && (start != null ? so.StartDate.Date == start : true) 
    && (end !=null ? so.EndDate.Date == end : true))
select so

Answer 3

Since you're &&'ing them, looks like you want : true instead of : false.

Answer 4

You can use conditional parameters.

Change:

where ((opType!= "0" ? so.Operation == int.Parse(opType) : false) 

To:

where ((opType!= "0" ? so.Operation == int.Parse(opType) : so.Operation == Operation) 

and so on...