/// <summary>
/// 指定 FilterKeyValueAction 集合获取 Lambda 表达式
/// </summary>
/// <typeparam name="TItem"></typeparam>
/// <param name="filters"></param>
/// <returns></returns>
public static Expression <Func <TItem, bool> > GetFilterLambda <TItem>(this IEnumerable <FilterKeyValueAction> filters)
{
Expression <Func <TItem, bool> >?ret = null;
var exp_p = Expression.Parameter(typeof(TItem));
var visitor = new ComboExpressionVisitor(exp_p);
foreach (var filter in filters)
{
var exp = filter.GetFilterLambda <TItem>();
if (ret == null)
{
ret = exp;
continue;
}
var left = visitor.Visit(ret.Body);
var right = visitor.Visit(exp.Body);
ret = filter.FilterLogic switch
{
FilterLogic.And => Expression.Lambda <Func <TItem, bool> >(Expression.AndAlso(left, right), exp_p),
_ => Expression.Lambda <Func <TItem, bool> >(Expression.OrElse(left, right), exp_p),
};
}
return(ret ?? (r => true));
}
/// <summary>
/// 表达式取 and 逻辑操作方法
/// </summary>
/// <typeparam name="TItem"></typeparam>
/// <param name="expressions"></param>
/// <param name="logic"></param>
/// <returns></returns>
private static Expression <Func <TItem, bool> > ExpressionAndLambda <TItem>(this IEnumerable <Expression <Func <TItem, bool> > > expressions, FilterLogic logic = FilterLogic.And)
{
Expression <Func <TItem, bool> >?ret = null;
if (expressions.Any())
{
var exp_p = Expression.Parameter(typeof(TItem));
var visitor = new ComboExpressionVisitor(exp_p);
foreach (var exp in expressions)
{
if (ret == null)
{
ret = exp;
continue;
}
var left = visitor.Visit(ret.Body);
var right = visitor.Visit(exp.Body);
ret = logic == FilterLogic.And
? Expression.Lambda <Func <TItem, bool> >(Expression.AndAlso(left, right), exp_p)
: Expression.Lambda <Func <TItem, bool> >(Expression.OrElse(left, right), exp_p);
}
}
return(ret ?? (r => true));
}
