如: System.Linq.Expressions.Expression<Func<Model.Pub.PVHistory, bool>> where = l
=> l.PVType == 4
&& l.PVTarget == "Guest";
var count = Factory.CreateInstance.PVHistoryDao.Count(where);如何拆成
System.Linq.Expressions.Expression<Func<Model.Pub.PVHistory, bool>>
where = l => l.PVType == 4;where +=l =>l.PVTarget == "Guest";
像这种多行的写法谢谢
=> l.PVType == 4
&& l.PVTarget == "Guest";
var count = Factory.CreateInstance.PVHistoryDao.Count(where);如何拆成
System.Linq.Expressions.Expression<Func<Model.Pub.PVHistory, bool>>
where = l => l.PVType == 4;where +=l =>l.PVTarget == "Guest";
像这种多行的写法谢谢
我要把
=> l.PVType == 4
&& l.PVTarget == "Guest";
这一句话拆分成两句来写谢谢
{
public static Expression<TFunc> And<TFunc>(this Expression<TFunc> expr1, Expression<TFunc> expr2)
{
if (expr1.ReturnType != typeof(bool) || expr2.ReturnType != typeof(bool))
throw new ArgumentException("both lambda expressions must return boolean type");
if (expr1.Parameters.Zip(expr2.Parameters, (p1, p2) => p1.Type == p2.Type).Any(x => x == false))
throw new ArgumentException("expr1 and expr2 must have exactly the same parameters"); var p = expr1.Parameters;
var left = Expression.Invoke(expr1, p);
var right = Expression.Invoke(expr2, p);
var expr = Expression.And(left, right);
return Expression.Lambda<TFunc>(expr, p);
}
}然后可以这样调用: Expression<Func<Model.Pub.PVHistory, bool>> where = l => l.PVType >= 4;
Expression<Func<Model.Pub.PVHistory, bool>> where2 = l=> l.PVTarget == "Guest"; where = where.And(where2);
var count = Factory.CreateInstance.PVHistoryDao.Count(where);
query = query.Where(...)
query = query.Where(...)
相当于query = xxx.Where(... && ...)类似的
query = xxxx
query1 = query.Where(...)
query2 = query.Where(...)
query = query1.Union(query2)
相当于query = xxx.Where(... || ...)
但是并不建议,因为逻辑运算并不是只有and,我既然要写扩展就必须考虑,会有OR,会有优先级,这样一来,你的要求无论对你自己还是调用者反而都并不便宜。所以处于我的角度来看,这种扩展比较无意义