原文：http://www.cnblogs.com/ahui/archive/2011/08/04/2127282.html
EF通用的分页实现:
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/// <summary>/// 根据条件分页获得记录/// </summary>/// <param name="where">条件</param>/// <param name="orderBy">排序</param>/// <param name="ascending">是否升序</param>/// <param name="pageIndex">当前页码</param>/// <param name="pageSize">每页大小</param>/// <param name="totalRecord">总记录数</param>/// <returns>记录列表</returns>public virtual List<T> GetMany(Expression<Func<T, bool>> where, string orderBy, bool ascending, int pageIndex, int pageSize, out int totalRecord)
{ totalRecord = 0;
where = where.And(u => u.Flag != (int)Flags.Delete);
var list = dbset.Where(where);
totalRecord = list.Count();
if (totalRecord <= 0) return new List<T>();
list = list.OrderBy(orderBy, ascending).Skip((pageIndex - 1) * pageSize).Take(pageSize);
return list.ToList();
} |
动态排序扩展:
public static IQueryable<T> OrderBy<T>(this IQueryable<T> source, string propertyName, bool ascending) where T : class
{ Type type = typeof(T);
PropertyInfo property = type.GetProperty(propertyName);
if (property == null)
throw new ArgumentException("propertyName", "Not Exist");
ParameterExpression param = Expression.Parameter(type, "p");
Expression propertyAccessExpression = Expression.MakeMemberAccess(param, property);
LambdaExpression orderByExpression = Expression.Lambda(propertyAccessExpression, param);
string methodName = ascending ? "OrderBy" : "OrderByDescending";
MethodCallExpression resultExp = Expression.Call(typeof(Queryable), methodName, new Type[] { type, property.PropertyType }, source.Expression, Expression.Quote(orderByExpression));
return source.Provider.CreateQuery<T>(resultExp);
} |
如果要通过Expression获取字段，可以使用以下代码:
/// <summary>/// 获取对应的字段名/// </summary>/// <typeparam name="TSource"></typeparam>/// <param name="keySelector"></param>/// <returns></returns>public static string GetMemberName<TSource, TKey>(Expression<Func<TSource, TKey>> keySelector)
{ string fieldName = null;
var exp = keySelector.Body as UnaryExpression;
if (exp == null)
{
var body = keySelector.Body as MemberExpression;
fieldName = body.Member.Name;
}
else
{
fieldName = (exp.Operand as MemberExpression).Member.Name;
}
return fieldName;
} |
多条件组合(参见老赵相关文章):
/// <summary>/// 统一ParameterExpression/// </summary>internal class ParameterReplacer : ExpressionVisitor
{ public ParameterReplacer(ParameterExpression paramExpr)
{
this.ParameterExpression = paramExpr;
}
public ParameterExpression ParameterExpression { get; private set; }
public Expression Replace(Expression expr)
{
return this.Visit(expr);
}
protected override Expression VisitParameter(ParameterExpression p)
{
return this.ParameterExpression;
}
}public static class PredicateExtensionses
{ 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>> And<T>(this Expression<Func<T, bool>> exp_left, Expression<Func<T, bool>> exp_right)
{
var candidateExpr = Expression.Parameter(typeof(T), "candidate");
var parameterReplacer = new ParameterReplacer(candidateExpr);
var left = parameterReplacer.Replace(exp_left.Body);
var right = parameterReplacer.Replace(exp_right.Body);
var body = Expression.And(left, right);
return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
}
public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> exp_left, Expression<Func<T, bool>> exp_right)
{
var candidateExpr = Expression.Parameter(typeof(T), "candidate");
var parameterReplacer = new ParameterReplacer(candidateExpr);
var left = parameterReplacer.Replace(exp_left.Body);
var right = parameterReplacer.Replace(exp_right.Body);
var body = Expression.Or(left, right);
return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
}
} |
调用示例:
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public static PagedList<UsersDTO> GetUsers(int pageIndex, int pageSize, string orderBy, bool ascending,
Companys company, string email, string nickName, bool? isAdmin, UserStatus userStatus)
{ PagedList<UsersDTO> result = new PagedList<UsersDTO>(pageIndex, pageSize);
int totalRecord = 0;
Expression<Func<Users, bool>> where = PredicateExtensionses.True<Users>();
if (company != Companys.All) where = where.And(u => u.Company == (int)company);
if (!string.IsNullOrEmpty(email)) where = where.And(u => u.Email.Contains(email));
if (!string.IsNullOrEmpty(nickName)) where = where.And(u => u.NickName.Contains(nickName));
if (isAdmin.HasValue)
{
if (isAdmin.Value) where = where.And(u => u.IsAdmin == 1);
else where = where.And(u => u.IsAdmin == 0);
}
if (userStatus != UserStatus.All) where = where.And(u => u.UserStatus == (int)userStatus);
if (string.IsNullOrEmpty(orderBy))
orderBy = MapHelper.GetMappedName<UsersDTO, Users>(u => u.UserId);
else
orderBy = MapHelper.GetMappedName<UsersDTO, Users>(orderBy);
List<Users> list = _usersDao.GetMany(where, orderBy, ascending, pageIndex, pageSize, out totalRecord);
result.TotalRecordCount = totalRecord;
foreach (var data in list)
{
result.Items.Add(Mapper.Map<Users, UsersDTO>(data));
}
return result;
} |
上述方法的缺点是无法针对2个字段一起排序，不过只要修改排序参数还是可以实现的！
另外这种分页查询只能针对一个表或者视图