Linq To Entity多条件or查询处理

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1.多条件OR使用实例：

//学费
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.添加扩展方法

    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 firstvar secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);// apply composition of lambda expression bodies to parameters from the first expressionreturn 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);}}

更多参考：

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

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