Question

我有一个使用linq的请求查询。该查询有多个where子句，表示与名称和城市匹配的项目的返回列表。下面是我用于多个where子句的代码段，但它返回空的项集。 wherefield包含名称，城市等字段名称列表 wherefieldValue包含字段值列表，如james; delhi

 var where = FilterLinq<T>.GetWherePredicate(wherefield, wherefieldvalue).Compile();
 items = items.Where(where).OrderByDescending(a => a.GetType().GetProperty(field).GetValue(a, null)).Skip

 public class FilterLinq<T>
 {
    public static Expression<Func<T, Boolean>> GetWherePredicate(string whereFieldList, string whereFieldValues)
    {
        //the 'IN' parameter for expression ie T=> condition
        ParameterExpression pe = Expression.Parameter(typeof(T), typeof(T).Name);

        //combine them with and 1=1 Like no expression
        Expression combined = null;
        if (whereFieldList != null)
        {
            string[] field = whereFieldList.Split(';');
            string[] fieldValue = whereFieldValues.Split(';');
            for (int i = 0; i < field.Count(); i++)
            {
                //Expression for accessing Fields name property
                Expression columnNameProperty = Expression.Property(pe, field[i]);

                //the name constant to match 
                Expression columnValue = Expression.Constant(fieldValue[i]);

                //the first expression: PatientantLastName = ?
                Expression e1 = Expression.Equal(columnNameProperty, columnValue);

                if (combined == null)
                {
                    combined = e1;
                }
                else
                {
                    combined = Expression.And(combined, e1);
                }
            }
        }

        //create and return the predicate
        return Expression.Lambda<Func<T, Boolean>>(combined, new ParameterExpression[] { pe });
    }
}

Answer 1

你的例子有效。当然它只适用于字符串属性，但我认为，这是你的用例。也许它没有做你想要实现的目标，因为你将你的子句与和结合起来，但实际上你确实希望用Or来做，jus改变这个代码行：

combined = Expression.And(combined, e1);

要

combined = Expression.Or(combined, e1);

linq中的动态多个where子句c＃

1 个答案: