linq-sort ORDER BY

Scenario : Sort the query out of the statement, such as by time and so on.

description : Sorts the collection by the specified expression; delay: Sorts the collection by the specified expression; delay, which is ascending by default, plus descending for descending, and the corresponding extension method is Order by and OrderByDescending

1. Simple Form

This example uses order-by to sort employees by hire date:

var =     from inch db. Employees    e.hiredate    select e;

Description: The default is ascending

2. With conditional form

Note: The order of where and order by is not important. In T-SQL, where and order by have strict location restrictions.

var =     from inch db. Orders    where= =  "London" by    o.freightselect o;

Statement Description: Use where and order by to sort by freight.

3. Descending sort

var =      from inch db. Products by    p.unitprice descending    select p;

4.ThenBy

Statement Description: Sort the customer by using a composite order by order:

var =     from inch db. Customers    c.city,    c.contactnameselect C;

Description: Sort by multiple expressions, such as by City first, and when City is sorted by ContactName. This sentence is written in a lambda expression like this:

var = = c.city )            = c.contactname). ToList ();

There is no ThenBy statement in T-SQL, which is still translated as an order by, so you can also use the following statement to express:

var =      db. Customers    =  c.contactname)    = c.city). ToList ();

It is important to note that when multiple order-by operations are made, the cascade is in reverse order. For descending, replace with the corresponding descending operator.

var =      db. Customers    =  c.city)    = c.contactname). ToList ();

It is necessary to note that the order by type is not supported, and anonymous classes are not supported. Like what

var =      db. Customers    =  new    {        c.city,        c.contactname    }). ToList ();

will be thrown out of the exception. The error is that the preceding operation has an anonymous class, and then, when followed by, the category is compared. Like what

var =      db. Customers    . Select = New    {        c.city,        c.address    })    = + c). ToList ();

If you want to use the order order (c + + c), the precondition is that the category of the resulting object must be the basic type of the C # language in the preceding step. For example, here City is a string type.

var =      db. Customers    . Select = c.city)     = + c). ToList ();

5.ThenByDescending

Both of these extension methods are used after orderby/orderbydescending, the first thenby/thenbydescending extension method as the second sort basis, and the second thenby/ ThenByDescending is used as a third-digit sort basis, and so on

var =     from inch db. Orders    where= =1    o.shipcountry, O.freight descending     Select o;

Statement Description: Order orders for EmployeeID 1 are ordered first by sending to the country and then by freight from high to low.

6. With GroupBy form

varQ=      fromPinchdb. ProductsGroupP byP.categoryid intoG. G.Key    Selectnew {G.Key, Mostexpensiveproducts=             fromP2inchgwhereP2. UnitPrice==G.Max(P3=P3. UnitPrice)SelectP2};

Statement Description: Use ORDER BY, Max, and group by to derive the highest unit price in each category and sort the products by CategoryID.

linq-sort ORDER BY