Let’s create a master page called Site.master and a web content form as demo.aspx.

    <title>Loading Demo</title>


    <form>
        
            
                
            
        

<div>

<!-- Page Header will go here... -->

</div>

<div>


                                            <!-- Page-specific content will go here... -->
                                        

</div>

<div>

<!-- Page Footer will go here... -->

</div>

<!-- Code to fetch data from a database -->

 
    try{
 var divLoadingMessage =  document.getElementById("divLoadingMsg")
 if (divLoadingMessage != null && typeof(divLoadingMessage) != 'undefined')
        {
            divLoadingMessage.style.display="none";
            divLoadingMessage.parentNode.removeChild(divLoadingMessage);
        }
    }catch(e){}

1. Using Dynamic Linq
2. Some work arround so that linq query can be generated at runtime.

Essentially 2nd approach is the same as that used in 1st one. But if you just want to implement sorting and do not want to digg into Dynamic Linq libraries you can follow the article…

Let’s assume following method expects sortExpression parameter directly passed by UI layer GridView.

public DataTable GetSomeData(par1, par2...., string sortExpression) { var query = (//Linq query goes here ) // We want something like this which is not possible as of now var query = (some query) (OrderBy SortExpression) }
Here is the extension method you would like to follow…
public DataTable GetSomeData(par1, par2...., string sortExpression) { var query = (//Linq query goes here ) // We want something like this which is not possible as of now var query = (some query) (OrderBy SortExpression) } public static Util { //Thanks to Ernesto for pointing out a small correction in method signature. public static IQueryable OrderBy(this IQueryable source, string sortExpression) where TEntity : class { var type = typeof(TEntity); // Remember that for ascending order GridView just returns the column name and for descending it returns column name followed by DESC keyword // Therefore we need to examine the sortExpression and separate out Column Name and order (ASC/DESC) string[] expressionParts = sortExpression.Split(' '); // Assuming sortExpression is like [ColoumnName DESC] or [ColumnName] string orderByProperty = expressionParts[0]; string sortDirection = "ASC"; string methodName = "OrderBy"; //if sortDirection is descending if (expressionParts.Length > 1 && expressionParts[1] == "DESC") { sortDirection = "Descending"; methodName += sortDirection; // Add sort direction at the end of Method name } var property = type.GetProperty(orderByProperty); var parameter = Expression.Parameter(type, "p"); var propertyAccess = Expression.MakeMemberAccess(parameter, property); var orderByExp = Expression.Lambda(propertyAccess, parameter); MethodCallExpression resultExp = Expression.Call(typeof(Queryable), methodName, new Type[] { type, property.PropertyType }, source.Expression, Expression.Quote(orderByExp)); return source.Provider.CreateQuery(resultExp); } }
Usage will be as of follows…
public DataTable GetSomeData(par1, par2...., string sortExpression) { var query = (//Linq query goes here ) // We want something like this which is not possible as of now var query = (some query) return query.OrderBy(SortExpression).ToDataTable(rec => new object[] { query})); }
Again OrderBy is an extension method. Hope this helps!

  

<!-- Some other code---->

1. Implement custom sorting.
2. Change IEnumerable datatype into one of these datatypes.

Here we will try to follow 2nd approach. In our data access layer we will change IEnumerable into a DataTable using an static utility class. Here is the code to perform that operation

public static class Util { public static DataTable ToDataTable(this IEnumerable varlist, CreateRowDelegate fn) { DataTable dtReturn = new DataTable(); // column names PropertyInfo[] oProps = null; // Could add a check to verify that there is an element 0 foreach (T rec in varlist) { // Use reflection to get property names, to create table, Only first time, others will follow if (oProps == null) { oProps = ((Type)rec.GetType()).GetProperties(); foreach (PropertyInfo pi in oProps) { // Note that we must check a nullable type else method will throw and error Type colType = pi.PropertyType; if ((colType.IsGenericType) && (colType.GetGenericTypeDefinition() == typeof(Nullable))) { // Since all the elements have same type you can just take the first element and get type colType = colType.GetGenericArguments()[0]; } dtReturn.Columns.Add(new DataColumn(pi.Name, colType)); } } DataRow dr = dtReturn.NewRow(); //Iterate through each property in PropertyInfo foreach (PropertyInfo pi in oProps) { // Handle null values accordingly dr[pi.Name] = pi.GetValue(rec, null) == null ? DBNull.Value : pi.GetValue(rec, null); } dtReturn.Rows.Add(dr); } return (dtReturn); } public delegate object[] CreateRowDelegate(T t); }
Changes in the Select method
public ISingleResult SelectMethod(){ //Get DAL Instance DALInstance return DALInstance.GetSomeData(){} } public DataTable GetSomeData() { ISingle result = //code to get result; return (result.ToDataTable(rec => new object[] { result})); }
As you can see ToDataTable is an extenstion method and will be available to all IEnumerable types.Obviously there are some performance overhead due to use of reflection but still this approach can be used. However for real time applications performance testing must be performed.

Hope this helps!

Friday, July 20, 2007

During development I encountered this problem. So here I am posting a solution for the same.
Suppose a reader is reading result set which normally returns fields ‘A’ ‘ B’ AND ‘C’ and in some cases it also returns ‘W’.So your dataread method is likeLet’s have some object for the data to persist.
Public Object DemoObject { //string Property A //string Property B //string Property C //string Property W //Constructor Object(string a, string b, string c) { A = a; B = b; C = c; W = string.Empty; } Object(string a, string b, string c, string w) { A = a; B = b; C = c; W = w; } } private DemoObject DataRead(SqlDataReader reader) { //Some Code // returns object as Object } private Object DataRead(SqlDataReader reader) { //Some Code // if(reader["A"]!=null) string a = reader.GetString("A"); if(reader["A"]!=null) string b = reader.GetString("B"); if(reader["A"]!=null) string c = reader.GetString("C"); //Following line of code throws IndexOutOfRangeException if(reader["W"]!=null) string w = reader.GetString("W"); //Some Code //...... returns new DemoObject(a,b,c,w); }
It has the GetOrdinal() method as well, but it throws an exception if the reader doesn’t contain the field.
So
the solution is to use GetSchemaTable. It returns a table holding the
schema of the reader. There is one row in the table for each column
returned in the reader, and the
columns
of the schema table define properties of the reader’s result set, such
as the column name, size, data type and so on. We need to filter the
rows in that table to just the row matching the column we want, theschema table holds 1 row per column. The easiest way
to do this is with the default view.
e.g. if I were looking for a row called “myrow” in a reader’s results,
I could do this
DataView myView = reader.GetSchemaTable().DefaultView;myView.RowFilter = “ColumnName = ‘myrow’ “;

So final set of code is

//Create a method which verifies if a column exists in a particular row being read by datareader private bool ColumnExists(SqlDataReader reader, string columnName) { reader.GetSchemaTable().DefaultView.RowFilter = "ColumnName= '" + columnName + "'"; return (reader.GetSchemaTable().DefaultView.Count > 0); } So now ReadData method will look like private Object DataRead(SqlDataReader reader) { //Some Code // if(reader["A"]!=null) string a = reader.GetString("A"); if(reader["A"]!=null) string b = reader.GetString("B"); if(reader["A"]!=null) string c = reader.GetString("C"); //Check only those columns where you have doubts if(ColumnExists(reader, "W")) { if( reader["W"]!=null) string w = reader.GetString("W"); } //Some Code //...... returns new DemoObject(a,b,c,w); }