CODEWITHSUNDEEP
c#stringlinqdereference
Omri Aharon
Omri Aharon

Reputation: 17064

How to dereference a string that might be null in LINQ

Let's say I need to compare an object to other objects stored in a table called Indexes in my DB. I need to compare by the object's X property, which is a string, but it might be null.

I also have to trim my comparedObject's X property before comparing. I tried to do the following:

List<Guid> Ids = DataContext.Indexes.Where(ci =>
                 (comparedObject.X != null && ci.X != null ? 
                 ci.X == comparedObject.X.Trim() :
                 (ci.X == null || ci.X == string.Empty) && (comparedObject.X == null || comparedObject.X == string.Empty))).Select(ci => ci.Id).ToList();

And even though comparedObjects.X is null it still throws a null reference exception for the comparedObject.X.Trim() expression.

I assume that happens due to the linq conversion?

Is there a prettier way to trim the X property without having to assign comparedObject.X an empty string in case it's null before the query ?

EDIT: I'd like to elaborate - this query was reduced for simplicity here, I am also comparing about 6 other properties. I'd like to keep this in 1 query and not separate to 2 queries that differ in the X property alone. Trimming outside the query is my current solution, I was hoping for a in-statement solution in case there is any :)

Thanks!

Upvotes: 4

Views: 1091

Answers (2)

Damith
Damith

Reputation: 63065

And even though comparedObjects.X is null it still throws a null reference exception for the comparedObject.X.Trim() expression.

you better do a null check before the linq statement 

if(comparedObject !=null && !string.IsNullorEmpty(comparedObject.X))
{
    // your code goes here 
}

below code 

(ci.X == null || ci.X == string.Empty) && (comparedObject.X == null || comparedObject.X == string.Empty)

can change to 

string.IsNullorEmpty(ci.X) && string.IsNullorEmpty(comparedObject.X)

And i would change code as below 

List<Guid> Ids = DataContext.Indexes.Where(ci =>
                 (string.IsNullorEmpty(ci.X) && string.IsNullorEmpty(comparedObject.X)) || ci.X == comparedObject.X.Trim())
                .Select(ci => ci.Id).ToList();

Upvotes: 3

Tim.Tang
Tim.Tang

Reputation: 3188

may be you can try:

List<Guid> Ids = DataContext.Indexes.Where(ci =>ci.X != null ? ci.X == comparedObject.X==null?"":comparedObject.X.Trim() :
                                 (comparedObject.X == null || comparedObject.X == null)))
                            .Select(ci => ci.Id).ToList();

Upvotes: 0

Related Questions