（转）Entity Framework4.1实现动态多条件查询、分页和排序

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