Hi all:

for example:
var res=db.tables.single(p=>p.columnName==3);

if the record exist, it works well, but if it doesn't exist, it will throw an exception, I don't think exception is a reasonable way to know there isn't a record exist in the database, so , how to handle the case if record doesn't exist?

thanks in advance..

Not sure what your datasource is but SQl provides the EXISTS() function for just such a situation.  If you use a stored procedure which contains this function then you'll not have to rely on exception handling to deal with this in your code pages.

 Regards

 SattaMassaGana

Get an sqldatareader.

and then use

imagine a reader object and command object

reader = cmd.ExecuteDataReader

if (reader.Read())

//Do stuff

it will only work if there is data.

Thanks for replying~

 Yes, I know, and also I could use :
var res=from ....where ....select .
via from & where & select , it won't throw exception if the record doesn't exist.

but since microsoft provide lambda, and lambda is simpler, I want to use lambda if possible,
now .... I think this is unbelivable , isn't it useless?

naturehermit:

Get an sqldatareader.

and then use

imagine a reader object and command object

reader = cmd.ExecuteDataReader

if (reader.Read())

//Do stuff

 

it will only work if there is data.

If you only need to know if it exists, how about the following:

var res = db.tables.Where(p => p.ColumnName==3).Count();

if (res>0) ...

This results in a Select Count(*) from Table Where ColumnName=@p0 query.

Instead of using the Single operator, use SingleOrDefault.  Or, you could use FirstOrDefault (as opposed to First).

Hello Joerattz:

  Thanks very much! Your answer is exactly.

 And also thanks others who have answered my question----thank you all! 

joerattz:

Instead of using the Single operator, use SingleOrDefault.  Or, you could use FirstOrDefault (as opposed to First).