C# 从 LINQ 查询结果集中填充 DataSet 或 DataTable
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Filling a DataSet or DataTable from a LINQ query result set
提问by Geoff Dalgas
How do you expose a LINQ query as an ASMX web service? Usually, from the business tier, I can return a typed DataSetor DataTablewhich can be serialized for transport over ASMX.
如何将 LINQ 查询公开为 ASMX Web 服务？通常，从业务层，我可以返回类型化的DataSet或DataTable可以序列化的以通过 ASMX 传输。
How can I do the same for a LINQ query? Is there a way to populate a typed DataSetor DataTablevia a LINQ query?
如何对 LINQ 查询执行相同的操作？有没有办法填充类型DataSet或DataTable通过 LINQ 查询？
public static MyDataTable CallMySproc()
{
string conn = "...";
MyDatabaseDataContext db = new MyDatabaseDataContext(conn);
MyDataTable dt = new MyDataTable();
// execute a sproc via LINQ
var query = from dr
in db.MySproc().AsEnumerable
select dr;
// copy LINQ query resultset into a DataTable -this does not work !
dt = query.CopyToDataTable();
return dt;
}
How can I get the result set of a LINQ query into a DataSetor DataTable? Alternatively, is the LINQ query serializable so that I can expose it as an ASMX web service?
如何将 LINQ 查询的结果集转换为 aDataSet或DataTable？或者，LINQ 查询是否可序列化，以便我可以将其公开为 ASMX Web 服务？
采纳答案by Jon Galloway
As mentioned in the question, IEnumerablehas a CopyToDataTablemethod:
正如问题中提到的，IEnumerable有一个CopyToDataTable方法：
IEnumerable<DataRow> query =
from order in orders.AsEnumerable()
where order.Field<DateTime>("OrderDate") > new DateTime(2001, 8, 1)
select order;
// Create a table from the query.
DataTable boundTable = query.CopyToDataTable<DataRow>();
Why won't that work for you?
为什么这对你不起作用？
回答by Dave Ward
If you use a return type of IEnumerable, you can return your queryvariable directly.
如果您使用 的返回类型IEnumerable，则可以直接返回您的查询变量。
回答by Brian Childress
Create a class object and return a list(T)of the query.
创建一个类对象并返回一个list(T)查询。
回答by Lars M?hlum
Make a set of Data Transfer Objects, a couple of mappers, and return that via the .asmx.
You should neverexpose the database objects directly, as a change in the procedure schema will propagate to the web service consumer without you noticing it.
制作一组数据传输对象，几个映射器，并通过 .asmx 返回。
您永远不应该直接公开数据库对象，因为过程架构中的更改将传播到 Web 服务使用者，而您不会注意到它。
回答by Lars M?hlum
To perform this query against a DataContextclass, you'll need to do the following:
要对DataContext类执行此查询，您需要执行以下操作：
MyDataContext db = new MyDataContext();
IEnumerable<DataRow> query =
(from order in db.Orders.AsEnumerable()
select new
{
order.Property,
order.Property2
})
as IEnumerable<DataRow>;
return query.CopyToDataTable<DataRow>();
Without the as IEnumerable<DataRow>;you will see the following compilation error:
如果没有，as IEnumerable<DataRow>;您将看到以下编译错误：
Cannot implicitly convert type 'System.Collections.Generic.IEnumerable' to 'System.Collections.Generic.IEnumerable'. An explicit conversion exists (are you missing a cast?)
无法将类型“System.Collections.Generic.IEnumerable”隐式转换为“System.Collections.Generic.IEnumerable”。存在显式转换（您是否缺少演员表？）
回答by Vijay S
If you use the return type of IEnumerable.It helps return your query variable directly.
如果您使用IEnumerable.It的返回类型，它有助于直接返回您的查询变量。
MyDataContext db = new MyDataContext();
IEnumerable<DataRow> query =
(from order in db.Orders.AsEnumerable()
select new
{
order.Property,
order.Property2
})
as IEnumerable<DataRow>;
return query.CopyToDataTable<DataRow>();
回答by Gabriel Magana
For the sake of completeness, these solutions do not work for EF Core (at least not for EF Core 2.2). Casting to IEnumerable<DataRow>, as suggested in the other answers here, fails. Implementing this class and extension methods worked for me https://docs.microsoft.com/en-us/dotnet/framework/data/adonet/implement-copytodatatable-where-type-not-a-datarow.
为完整起见，这些解决方案不适用于 EF Core（至少不适用于 EF Core 2.2）。铸造到IEnumerable<DataRow>，如这里的其他答案建议，将失败。实现此类和扩展方法对我有用 https://docs.microsoft.com/en-us/dotnet/framework/data/adonet/implement-copytodatatable-where-type-not-a-datarow。
Why it's not built into EF Core, I have not idea.
为什么它没有内置到 EF Core 中，我不知道。
