IQueryable:动态创建或筛选

我有一套搜索标准,格式如下:

 member  |  value  |  operator
 --------+---------+---------
 height  |   10    |    >
 height  |    2    |    < 
 name    |  Carl   |   ==

我想查询所有符合这些条件的对象。

• 为每一个构建表达式 标准的
• 表达
• 包含 串联表达式

你知道一个最简单的方法来过滤一个普通的IQueryable收集使用连续或连续的?

基于 IlyaBuiluk solution @ CodeProject

// The structure used by the new extension method
public struct SearchCriteria
{
    public string Column;
    public object Value;
    public WhereOperation Operation;
}

// How to convert the rules structure to the search criteria structure
var searchCriterias = grid.Where.rules.Select(Rule => new SearchCriteria
  {
      Column = Rule.field,
      Operation =
          (WhereOperation)
          StringEnum.Parse(
              typeof (WhereOperation),
              Rule.op),
      Value = Rule.data
  }).ToArray();


// Usage:
query = query.WhereOr(searchCriterias);


// Implementation
public static IQueryable<T> WhereOr<T>( this IQueryable<T> Query, SearchCriteria [ ] Criterias )
{
    if( Criterias.Count( ) == 0 )
        return Query;

    LambdaExpression lambda;
    Expression resultCondition = null;

    // Create a member expression pointing to given column
    ParameterExpression parameter = Expression.Parameter( Query.ElementType, "p" );

    foreach( var searchCriteria in Criterias )
    {
        if( string.IsNullOrEmpty( searchCriteria.Column ) )
            continue;

        MemberExpression memberAccess = null;
        foreach( var property in searchCriteria.Column.Split( '.' ) )
            memberAccess = MemberExpression.Property
                ( memberAccess ?? ( parameter as Expression ), property );

        // Change the type of the parameter 'value'. it is necessary for comparisons (specially for booleans)
        ConstantExpression filter = Expression.Constant
            (
                Convert.ChangeType( searchCriteria.Value, memberAccess.Type )
            );

        //switch operation
        Expression condition = null;
        switch( searchCriteria.Operation )
        {
            //equal ==
            case WhereOperation.Equal:
                condition = Expression.Equal( memberAccess, filter );
                break;
            //not equal !=
            case WhereOperation.NotEqual:
                condition = Expression.NotEqual( memberAccess, filter );
                break;
            // Greater
            case WhereOperation.Greater:
                condition = Expression.GreaterThan( memberAccess, filter );
                break;
            // Greater or equal
            case WhereOperation.GreaterOrEqual:
                condition = Expression.GreaterThanOrEqual( memberAccess, filter );
                break;
            // Less
            case WhereOperation.Less:
                condition = Expression.LessThan( memberAccess, filter );
                break;
            // Less or equal
            case WhereOperation.LessEqual:
                condition = Expression.LessThanOrEqual( memberAccess, filter );
                break;
            //string.Contains()
            case WhereOperation.Contains:
                condition = Expression.Call( memberAccess,
                                            typeof( string ).GetMethod( "Contains" ),
                                            Expression.Constant( searchCriteria.Value ) );
                break;

            default:
                continue;
        }

        resultCondition = resultCondition != null ? Expression.Or( resultCondition, condition ): condition;
    }

    lambda = Expression.Lambda( resultCondition, parameter );

    MethodCallExpression result = Expression.Call(
               typeof( Queryable ), "Where",
               new [ ] { Query.ElementType },
               Query.Expression,
               lambda );

    return Query.Provider.CreateQuery&lt;T&gt;( result );

}