LinQ query - Add Where dynamically - linq

Question

I am having a hard time solving this problem, need code for creating a dynamic linq query in C#, asp.net. I have 5 dropdown list that searches different column in same database table and return item filtered value to a single listbox. The problem is there is no sequence that which or all or any will be selected in DDLs but the combined filtered result should show up in listbox. I have a working query that is searching and returning result in one column at a time for each DDL selection separately. Have to add where clauses with AND to add other DDL selections dynamically to this query. Thanks
public ListItemCollection searchProject(ListItemCollection projList, String searchstr, String columnName)
{
DataSet DSToReturn = new DataSet();
ListItemCollection returnItems = new ListItemCollection();
DataTable results = (from d in ((DataSet)_MyDataset).Tables["Records"].AsEnumerable()
orderby d.Field<string>("Name") ascending
where (d.Field<string>(columnName) != null)
where d[columnName].ToString().ToLower().Contains(searchstr.ToLower())
select d).CopyToDataTable();
foreach (ListItem li in projList)
{
if ((from System.Data.DataRow row in results.Rows
where li.Value.Equals(row["value"].ToString(), StringComparison.InvariantCultureIgnoreCase)
select row["value"]).Count() > 0)
returnItems.Add(li);
}
return returnItems;
}

Answer 1

Here's some example code for how we do it ...
private void DataPortal_Fetch(GoalCriteria criteria)
{
using (var ctx = ContextManager<Data.ExodusDataContext>
.GetManager(Database.ApplicationConnection, false))
{
this.RaiseListChangedEvents = false;
this.IsReadOnly = false;
// set option to eager load child object(s)
var opts = new System.Data.Linq.DataLoadOptions();
opts.LoadWith<Data.Goal>(row => row.Contact);
opts.LoadWith<Data.Goal>(row => row.Sales);
opts.LoadWith<Data.Goal>(row => row.Customer);
ctx.DataContext.LoadOptions = opts;
IQueryable<Data.Goal> query = ctx.DataContext.Goals;
if (criteria.Name != null) // Name
query = query.Where(row => row.Name.Contains(criteria.Name));
if (criteria.SalesId != null) // SalesId
query = query.Where(row => row.SalesId == criteria.SalesId);
if (criteria.Status != null) // Status
query = query.Where(row => row.Status == (int)criteria.Status);
if (criteria.Statuses.Count != 0) // Statuses
query = query.Where(row => criteria.Statuses.Contains((GoalStatus)row.Status));
if (criteria.ContactId != null) // ContactId
query = query.Where(row => row.ContactId == criteria.ContactId);
if (criteria.CustomerId != null) // CustomerId
query = query.Where(row => row.CustomerId == criteria.CustomerId);
if (criteria.ScheduledDate.DateFrom != DateTime.MinValue) // ScheduledDate
query = query.Where(t => t.ScheduledDate >= criteria.ScheduledDate.DateFrom);
if (criteria.ScheduledDate.DateTo != DateTime.MaxValue)
query = query.Where(t => t.ScheduledDate <= criteria.ScheduledDate.DateTo);
if (criteria.CompletedDate.DateFrom != DateTime.MinValue) // ComplatedDate
query = query.Where(t => t.CompletedDate >= criteria.CompletedDate.DateFrom);
if (criteria.CompletedDate.DateTo != DateTime.MaxValue)
query = query.Where(t => t.CompletedDate <= criteria.CompletedDate.DateTo);
if (criteria.MaximumRecords != null) // MaximumRecords
query = query.Take(criteria.MaximumRecords.Value);
var data = query.Select(row => GoalInfo.FetchGoalInfo(row));
this.AddRange(data);
this.IsReadOnly = true;
this.RaiseListChangedEvents = true;
}
}
We just check for a null value assigned to our criteria object, if it's not null then we append it to the query.