entityframework多条件查询类
var dataaccess = new BaseAccess();int totalCount = 0;var paramS = new OrderModelField[1];paramS[0].IsDesc = true;paramS[0].PropertyName = "B_Email";Expression<Func<Rm_Sec_UserData, bool>> expr = PredicateExtensions.True<Rm_Sec_UserData>().And(t => t.F_Email.Equals(pUserEmail)).And(t => t.F_UserPass == pPassword);var list = dataaccess.GetListPaged(1, 2,expr, out totalCount, paramS);//
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>> 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);}
}
/// <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;}
}
