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[数据库]【转】关于LinQ的动态Or查询


/// <summary>/// 构造函数使用True时:单个AND有效,多个AND有效;单个OR无效,多个OR无效;混合时写在AND后的OR有效/// 构造函数使用False时:单个AND无效,多个AND无效;单个OR有效,多个OR有效;混合时写在OR后面的AND有效/// </summary>public static class PredicateExtensions{  public static Expression<Func<T, bool>> True<T>() { return f => true; }  public static Expression<Func<T, bool>> False<T>() { return f => false; }  public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expression1, Expression<Func<T, bool>> expression2)  {    var invokedExpression = Expression.Invoke(expression2, expression1.Parameters.Cast<Expression>());    return Expression.Lambda<Func<T, bool>>(Expression.Or(expression1.Body, invokedExpression), expression1.Parameters);  }  public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expression1, Expression<Func<T, bool>> expression2)  {    var invokedExpression = Expression.Invoke(expression2, expression1.Parameters.Cast<Expression>());    return Expression.Lambda<Func<T, bool>>(Expression.And(expression1.Body, invokedExpression), expression1.Parameters);  }}

 

调用方法:

HUBDataDataContext db = new HUBDataDataContext();var predicate = PredicateExtensions.False <T_DISPATCH>();predicate = predicate.Or(c => c.ToHUBID == 1);var dispatch = db.T_DISPATCH.Where(predicate).Where(c => c.State == 3); 

 

转自:http://www.cnblogs.com/ejiyuan/archive/2009/07/14/1523515.html