Checking if an object exists in an SQL table based on a Column and some object's Field

Question

I am currently trying to check if there exists an instance of an object with a unique ID in a SQL Table. So as to not place duplicates. Here is a sample of what I currently have:

string ui = someObj.getUniqueID();

IQueryable<String> checkDataQuery = from cdq in db.SomeObjects
                                           where cdq.UniqueID == ui
                                           select cdq.UniqueID;

if (checkDataQuery != ui) // This is just my attempt at making sure that
                          // the query actually returned something and not 
                          // the string representing nothing found, so if there
                          // is a better checking method that would even more helpful.

The main issue I am running into is that I can not access checkDataQuery as a string. I attempted casting it, and using the .Single()/.First() methods, however, the former had no success, and the latter made the single string being returned into a list of characters.

Habib · Accepted Answer · 2014-03-24 14:55:42Z

2

You can check the result with Enumerable.Any like:

bool ifExists = db.SomeObjects.Any(r=> r.UniqueID == ui);

If you want to get the object, then you can use FirstOrDefault and check for null like:

var dbObject = db.SomeObjects.FirstOrDefault(r=> r.UniqueID == ui);
if(dbObject != null)
{
  //record exists
}

answered Mar 24, 2014 at 14:55

Habib

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2 Comments

JVB Over a year ago

I am still fairly new to C# and Linq, if you could, can you explain the "=>" operator, the rest reads fairly straightforward.

Habib Over a year ago

@FenrirProtocol, LINQ uses two styles , method syntax and query syntax. What I have used is method syntax. => used in the code is basically a Lambda Expression

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