LINQ and C#
LINQ provides many of the common SQL operations, such as join queries, grouping, aggregation, and sorting of results. In addition, it allows you to use the object-oriented features of C# in query expressions and processing, such as hierarchical query results.
Joining
You will often want to search for objects from more than one data source. LINQ provides the join
clause that offers the ability to join many data sources, not all of which need be databases. Suppose you have a list of customers containing customer names and email addresses, and a list of customer home addresses. You can use LINQ to combine both lists to produce a list of customers, with access to both their email and home addresses:
from customer in customers join address in addresses on customer.Name equals address.Name ...
The join
condition is specified in the on
subclause, similar to SQL, except that the objects joined need not be tables or views in a database. The join
class syntax is:
[data source 1] join [data source 2] on [join condition]
Here, we are joining two data sources, customers and addresses, based on the customer name properties in each object. In fact, you can join more than two data sources using a combination of join
clauses:
from customer in customers join address in addresses on customer.Name equals address.Name join invoice in invoices on customer.Id equals invoice.CustomerId join invoiceItem in invoiceItems on invoice.Id equals invoiceItem.invoiceId
A LINQ join clause returns a result ...
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