Question

Based on the documentation here:
http://docs.composite.net/Data/AccessingDataWithCSharp/How-to-Query-Data-Using-LINQ#_How_to_Query

I need to query data in a table using a filter in type string[int1,int2,int3..] and can’t work out how to go about it.

The string[] comes from a different table field which stores id values of a multiselect element on a form:

Table ‘Profile‘ (AGlobal.profile) contains columns:

Id   Types(profile_accomtypes)
1    1,2
2    4,7
3    12,4,6
4    3,6,9

Then I have a static table ‘TypeDesc’ (ALocal.proptype) listing a total of 12 ‘Type’ values:

Id   Description(proptype_names)
1     The first description
2     The second description
........
12    The twelfth description

I created a strongly coded class enabling me to easily handle the form content on submit from the client. Within the form was a couple of multiselects (one of them being ‘Types” above in the Profile datatype table.) Each of the multiselects are passed to the server in serialized JSON format where I string.Join the ‘Types’ values with a comma separator to save into the Profile.Types column.

Now I want to serve the selections in a profile page to the client by loading the Types string[] of Profile Id and using the int id values to filter the TypeDesc table to only select the Type values with Description so that I can render the descriptions as a bullet list on the client.

The filter Types in the Profile table are always id integers
My code I’m using is:

var myProftype =
   (from d in connection.Get<AGlobal.profile>() // find multiselected type string values
   where d.Id == StUserSet.utoken
   select d).First();
   string sProftype = myProftype.profile_accomtypes;                
   string[] sTypes = sProftype.Split(',');

// now filter proptypes to sTypes
var myTAccomtypes =
   (from d in connection.Get<ALocal.proptype>() // get all the types from the DB
   where(r => sTypes.Contains(r.Field<int>("Id"))) //Lambda ?
   select d).All;

StringBuilder sb = new StringBuilder(0); //create a bullet list string
// Loop over strings
    foreach (string s in myTAccomtypes)
    {
          sb.append("<dd>"+ s +"</dd>");
    }
   TuAccomtypes = sb.ToString();  // pass string to JQuery Taconite as part of AJAX response to alter DOM.

I have an error on the Lambda trying to filter my types.
In VS2010:

Error = Cannot convert lambda expression to type bool because its not a delegate type.

I also do not know how to go about parsing the sTypes variables to int (if I need to) so that the filter works 🙁

Where am I going wrong? Is there a cleaner way to filter a dataset against a comma separated list queried from a column field within a db table?

Thank you for any help/ideas in advance.
Martin.

Answer 1

Once splitting the string var from the original Linq query (which identified a single field with a joined string of comma separated id numbers.) I wasn’t able to use “Contains” properly.
I cast the second Linq query ToList which evaluated the collection.

Then instead of working with a full result I limited the result to just the id and name fields.

Relying on an article posted by Vimal Lakhera:

http://www.c-sharpcorner.com/uploadfile/VIMAL.LAKHERA/convert-a-linq-query-resultset-to-a-datatable/
I converted the result set into a DataTable which allowed easy looping and selection of fields to output as an html string as part of a JQuery Taconite callback.

Here’s what works for me…

// now filter proptypes to selected Types|
var myTAccomtypes = from d in connection.Get<ALocal.proptype>().ToList()
    // ToList() will evaluate collection, you cannot pass sTypes array of integers to a sql query, at least not in that way
    where sTypes.Contains(d.proptype_id.ToString())
    select new { d.proptype_id, d.proptype_name };

    DataTable AcomType = LINQToDataTable(myTAccomtypes);

    StringBuilder sb = new StringBuilder();
    // Loop over table rows
    foreach (var row in AcomType.Rows.OfType<DataRow>().Take(19))  // will .Take up to a maximum of x rows from above
    {
         sb.Append("<dd>");
         sb.Append(row["proptype_name"].ToString());
         sb.Append("</dd>");
     }
     HldUserSet.TuAccomtypes = sb.ToString();
     //HldUserSet.TuAccomtypes = string.Join(",", myTAccomtypes); //Check query content

Using Vimal’s ‘LINQToDataTable” with the tweak in the LINQ request means that I can use the class in numerous places of the site very quickly.

This works a treat for those with a single string of joined id’s in the form of “2,7,14,16” that need to be split and then used to filter against a wider collection matching the id’s from the string to record id numbers in a different collection.