trying to query using custom comparer

Question

Hey, 

I'm trying to query an Azure Storage Table using a custom RowKey comparer that basically splits the RowKey and compares each
string separately (in order to get rows by only as part of the key matching,with out knowing the amount of parts the key has).

I've tried the following but got an exception of "The expression value is not supported".

// the actual query
var q = from row in DataContext.CreateQuery<WorkItem>(TableName)
                            where CustomCompare(p_strRowPK,entity.RowKey)
                            select row ;

// and the compare method
private bool CustomCompare(string p_strFilterRowKey, string p_strTestedRowKey)
            {
                string[] arrFilterValues = p_strFilterRowKey.Split(new string[] { "," }, StringSplitOptions.RemoveEmptyEntries);
                string[] arrTestedValues = p_strFilterRowKey.Split(new string[] { "," }, StringSplitOptions.RemoveEmptyEntries);

                int intEqualityCounter = 0;

                if (arrFilterValues.Length == arrTestedValues.Length)
                {
                    for (int intCurrentIndex = 0; intCurrentIndex < arrTestedValues.Length; intCurrentIndex++)
                    {
                        // They are either equal or the filter is empty for a certain value
                        if (arrFilterValues[intCurrentIndex] != string.Empty || arrTestedValues[intCurrentIndex] == arrFilterValues[intCurrentIndex])
                        {
                            intEqualityCounter++;
                        }
                    }
                }
                
                return intEqualityCounter == arrFilterValues.Length && intEqualityCounter == arrTestedValues.Length;
            }

Is there an easy way to make this work, or do i have to do this explicitly ?

Answer 1

Hi,

Your Linq query is formatted wrongly I think.

var q = from row in DataContext.CreateQuery<WorkItem>(TableName)
            where CustomCompare(p_strRowPK,row.RowKey)
            select row;

would be equal to:

var q = from row in DataContext.CreateQuery<WorkItem>(TableName)
            where true         
            select row ;

This is not a valid Linq query. I think you should write something like:

var q = from row in DataContext.CreateQuery<WorkItem>(TableName)
           where row.RowKey.CustomCompare(p_strRowPK) == true        
            select row ;

You'll have to make ann extension method of the CustomCompare method for the String type of course:

public static bool CustomCompare(this string p_strTestedRowKey, string p_strFilterRowKey)
            {
                string[] arrFilterValues = p_strFilterRowKey.Split(new string[] { "," }, StringSplitOptions.RemoveEmptyEntries);
                string[] arrTestedValues = p_strFilterRowKey.Split(new string[] { "," }, StringSplitOptions.RemoveEmptyEntries);

                int intEqualityCounter = 0;

                if (arrFilterValues.Length == arrTestedValues.Length)
                { for (int intCurrentIndex = 0; intCurrentIndex < arrTestedValues.Length; intCurrentIndex++)
                    {
                        // They are either equal or the filter is empty for a certain value
                        if (arrFilterValues[intCurrentIndex] != string.Empty || arrTestedValues[intCurrentIndex] == arrFilterValues[intCurrentIndex])
                        {
                            intEqualityCounter++;
                        }
                    }
                }
               
                return intEqualityCounter == arrFilterValues.Length && intEqualityCounter == arrTestedValues.Length;
            }

---

With regards,

Patriek

www.patriekvandorp.net

---

If this reply is of help to you, please don't forget to mark it as an answer.

Answer 2

Hey, That's not the problem.
I get a runtime exception that the following message

The expression value CustomCompare("10101", [10007].RowKey) is not supported

which leads me to think that somehow linq fails to parse the query

Answer 3

Composite partition keys or row keys is not supported in the manner suggested by your implementation. In this case, the LINQ query cannot be translated to a query string suitable for Azure table storage. In the case for a composite key, you query should be something like RowKey >= “ xxx“ && RowKey <=  “yyy” where “xxx” and “yyy” are sub keys. So, yes you need to do this explicitly.

I have written an alternate Azure table storage client, Lucifure Stash, which supports many abstractions including composite keys. Lucifure Stash also supports large data columns > 64K, arrays & lists, enumerations, out of the box serialization, user defined morphing, public and private properties and fields and more.
It is available free for personal use at http://www.lucifure.com  or via NuGet.com.