Linq To SQL : How to order with a string typed expression ?

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);

}