Join (keyword)

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The most powerful and most complex query operator is join, which allows you to combine sources from two separate sequences into one result sequence.

For example:

var greet := from cust in MyCustomers
  join cntry in Countries on cust.Country equals cntry.Name
  select cntry.Greeting+' '+cust.Name;

This query would then return a sequence of strings such as "Hello Paul", "Bonjour, Jean-Pierre", and so on.

If the join is not followed by a select, its result will return anonymous types containing both of the joined sequences, similar to having specified "select cust, cntry". join can be followed by the into keyword to give a name to the new sequence, so it can be referenced further down in the query, such as:

var l := from cust in MyCustomers
  join cntry in Countries on cust.Country equals cntry.Name into j
  where j.cust.City = 'Berlin' and j.cntry.Continent = 'Europe';

This query would a list of all Customer/Country entries where the customer lives in a city named Berlin located in Europe (it will not return customers in Berlin, Wisconsin).

See Also

• Query Expressions

Area: Oxygene Language
Compiler version: Oxygene 5

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