After using Linq To SQL queries, I was quickly confronted to sort my data with a string expression provided, for example, by a gridview when a user require it. At this moment, I understood that the strongly typed system used with Linq cannot help me for this task… Understanding the fact that allowing a string expression representing an object property is contrary to Linq purpose, I began to search with our best friend ”Google” a soluce to resolve quickly my problem. But the best that I can obtain was a “switch case solution” which, according to the string property name, build the linq query sort filter with the associated object property. Immediatly, I guess my switch case code with 8-10 columns… No…
So, I started to write an extended method “OrderBy” allowing to take a string sort expression. Here the result.
/// <summary>
/// Extends method which allow to sort by string field name.
/// Allow to use a relative object definition for sorting (ex:LinkedObject.FieldsName1)
/// </summary>
/// <typeparam name=”TEntity”>Current Object type for query</typeparam>
/// <param name=”source”>list of defined object</param>
/// <param name=”sortExpression”>string name of the field we want to sort by</param>
/// <returns>Query sorted by sortExpression</returns>
public static IQueryable<TEntity> OrderBy<TEntity>(
this IQueryable<TEntity> 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 [ColumnName 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
}
MethodCallExpression resultExp = null;
if (!orderByProperty.Contains(“.”))
{
var property = type.GetProperty(orderByProperty);
var parameter = Expression.Parameter(type, “p”);
var propertyAccess = Expression.MakeMemberAccess(parameter, property);
var orderByExp = Expression.Lambda(propertyAccess, parameter);
resultExp = Expression.Call(typeof(Queryable), methodName,
new Type[] { type, property.PropertyType },
source.Expression, Expression.Quote(orderByExp));
}
else
{
Type relationType = type.GetProperty(orderByProperty.Split(‘.’)[0]).PropertyType;
PropertyInfo relationProperty = type.GetProperty(orderByProperty.Split(‘.’)[0]);
PropertyInfo relationProperty2 = relationType.GetProperty(orderByProperty.Split(‘.’)[1]);
var parameter = Expression.Parameter(type, “p”);
var propertyAccess = Expression.MakeMemberAccess(parameter, relationProperty);
var propertyAccess2 = Expression.MakeMemberAccess(propertyAccess, relationProperty2);
var orderByExp = Expression.Lambda(propertyAccess2, parameter);
resultExp = Expression.Call(typeof(Queryable), methodName,
new Type[] { type, relationProperty2.PropertyType },
source.Expression, Expression.Quote(orderByExp));
}
return source.Provider.CreateQuery<TEntity>(resultExp);
}
/// <summary>
/// Allow to add another sorting on a query with a string representation of the field to sort by.
/// </summary>
/// <typeparam name=”TEntity”>Current Object type for query</typeparam>
/// <param name=”source”>list of defined object</param>
/// <param name=”sortExpression”>string name of the field we want to sort by</param>
/// <returns>Query sorted by sortExpression</returns>
public static IOrderedQueryable<TEntity> ThenBy<TEntity>(
this IOrderedQueryable<TEntity> 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 [ColumnName DESC] or [ColumnName]
string orderByProperty = expressionParts[0];
string sortDirection = “ASC”;
string methodName = “ThenBy”;
//if sortDirection is descending
if (expressionParts.Length > 1 && expressionParts[1] == “DESC”)
{
sortDirection = “Descending”;
methodName += sortDirection; // Add sort direction at the end of Method name
}
MethodCallExpression resultExp = null;
if (!orderByProperty.Contains(“.”))
{
var property = type.GetProperty(orderByProperty);
var parameter = Expression.Parameter(type, “p”);
var propertyAccess = Expression.MakeMemberAccess(parameter, property);
var orderByExp = Expression.Lambda(propertyAccess, parameter);
resultExp = Expression.Call(typeof(Queryable), methodName,
new Type[] { type, property.PropertyType },
source.Expression, Expression.Quote(orderByExp));
}
else
{
Type relationType = type.GetProperty(orderByProperty.Split(‘.’)[0]).PropertyType;
PropertyInfo relationProperty = type.GetProperty(orderByProperty.Split(‘.’)[0]);
PropertyInfo relationProperty2 = relationType.GetProperty(orderByProperty.Split(‘.’)[1]);
var parameter = Expression.Parameter(type, “p”);
var propertyAccess = Expression.MakeMemberAccess(parameter, relationProperty);
var propertyAccess2 = Expression.MakeMemberAccess(propertyAccess, relationProperty2);
var orderByExp = Expression.Lambda(propertyAccess2, parameter);
resultExp = Expression.Call(typeof(Queryable), methodName,
new Type[] { type, relationProperty2.PropertyType },
source.Expression, Expression.Quote(orderByExp));
}
return (IOrderedQueryable<TEntity>)source.Provider.CreateQuery<TEntity>(resultExp);
}
