Question

对于复杂的查询来说，编写LINQ查询是不是很容易？

select a.sNavID,
       a.sNavText,
       a.sNavText as EName,
       ' '+a.sNavText as NameDisplay 
from ContentPageNav as a 
where a.navID=0 
union 
select b.sNavID,
       a.sNavText + ' >> ' + b.sNavText as Name,
       b.sNavText as EName,
       ' ' + b.sNavText as NameDisplay 
from ContentPageNav as a 
inner join ContentPageNav as b on a.sNavID=b.navID and b.catNo=1
union 
select c.sNavID,a.sNavText + ' >> ' + b.sNavText + ' >> ' + c.sNavText as Name, 
       c.sNavText as EName,
       ' ' + c.sNavText as NameDisplay 
from ContentPageNav as a 
inner join ContentPageNav as b on a.sNavID=b.navID and b.catNo=1 
inner join ContentPageNav as c on b.sNavID=c.navID and c.catNo=2

Answer 1

LINQ几乎可以处理和查询你想要抛出它。

...完全组合的查询...

var query = (
    from a in ContentPageNav
    where a.navID == 0
    select new
    {
        a.sNavID,
        Name = a.sNavText,
        EName = a.sNavText,
        NameDisplay = " " + a.sNavText,
    }).Concat(
    from a in ContentPageNav
    join b in ContentPageNav on a.navID equals b.navID
    where b.catNo == 1
    select new
    {
        b.sNavID,
        Name = a.sNavText + " >> " + b.sNavText,
        EName = b.sNavText,
        NameDisplay = " " + b.sNavText,
    }).Concat(
    from a in ContentPageNav
    join b in ContentPageNav on a.navID equals b.navID
    where b.catNo == 1
    join c in ContentPageNav on b.navID equals c.navID
    where b.catNo == 1
    select new
    {
        c.sNavID,
        Name = a.sNavText + " >> " + b.sNavText + " >> " + c.sNavText,
        EName = c.sNavText,
        NameDisplay = " " + c.sNavText,
    });

...这是一个已经分解成较小部分的版本......

var rootRecords = ContentPageNav.Where(r => r.navID == 0);
var cat1Records = ContentPageNav.Where(r => r.catNo == 1);
var cat2Records = ContentPageNav.Where(r => r.catNo == 2);

var rootComposed =
    from a in rootRecords
    select new
    {
        a.sNavID,
        Name = a.sNavText,
        EName = a.sNavText,
        NameDisplay = " " + a.sNavText,
    };
var cat1Composed =
    from a in rootRecords
    join b in cat1Records on a.navID equals b.navID
    select new
    {
        b.sNavID,
        Name = a.sNavText + " >> " + b.sNavText,
        EName = b.sNavText,
        NameDisplay = " " + b.sNavText,
    };
var cat2Composed =
    from a in rootRecords
    join b in cat1Records on a.navID equals b.navID
    join c in cat2Records on b.navID equals c.navID
    select new
    {
        c.sNavID,
        Name = a.sNavText + " >> " + b.sNavText + " >> " + c.sNavText,
        EName = c.sNavText,
        NameDisplay = " " + c.sNavText,
    };

var composedQuery = rootComposed.Concat(cat1Composed).Concat(cat2Composed);

Answer 2

您刚刚使用了SQL anti-pattern #1。

对于复杂的查询来说，编写LINQ查询是不是很容易？

当使用Linq进行数据访问时，人们倾向于编写简单的查询来完成工作。首先编写复杂查询是错误的。从这个意义上说，这是事实。 SQL也是如此。

为复杂的查询编写LINQ查询是不是很容易？

2 个答案: