Linq To Entity多條件or查詢處理

1.多條件OR使用執行個體：

//學費
if (string.IsNullOrEmpty(tuition) == false && tuition != "0")
{
    Expression<Func<School, bool>> orQuery = q => false;
    foreach (var item in tuitionID)
    {
        Tuition tui = Tuition.GetMode(item);
        orQuery = orQuery.Or(q => q.TuitionFee >= tui.MinValue && q.TuitionFee < tui.MaxValue);
    }
    query = query.Where(orQuery);
}
           

2.添加擴充方法

public static class Utility
    {
        public static Expression<T> Compose<T>(this Expression<T> first, Expression<T> second, Func<Expression, Expression, Expression> merge)
        {
            // build parameter map (from parameters of second to parameters of first)
            var map = first.Parameters.Select((f, i) => new { f, s = second.Parameters[i] }).ToDictionary(p => p.s, p => p.f);
            // replace parameters in the second lambda expression with parameters from the first
            var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);
            // apply composition of lambda expression bodies to parameters from the first expression
            return Expression.Lambda<T>(merge(first.Body, secondBody), first.Parameters);
        }
        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
        {
            return first.Compose(second, Expression.And);
        }
        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
        {
            return first.Compose(second, Expression.Or);
        }
    }
    public class ParameterRebinder : ExpressionVisitor
    {

        private readonly Dictionary<ParameterExpression, ParameterExpression> map;
        public ParameterRebinder(Dictionary<ParameterExpression, ParameterExpression> map)
        {
            this.map = map ?? new Dictionary<ParameterExpression, ParameterExpression>();
        }

        public static Expression ReplaceParameters(Dictionary<ParameterExpression, ParameterExpression> map, Expression exp)
        {
            return new ParameterRebinder(map).Visit(exp);
        }
        protected override Expression VisitParameter(ParameterExpression p)
        {
            ParameterExpression replacement;
            if (map.TryGetValue(p, out replacement))
            {
                p = replacement;
            }
            return base.VisitParameter(p);
        }
    }
           

更多參考：

https://blogs.msdn.microsoft.com/meek/2008/05/02/linq-to-entities-combining-predicates/

http://www.cnblogs.com/blackice/archive/2013/01/08/2851424.html