/ doc / DocFrag / ARCQuery.ForeignKey / Attribute

Attribute

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AssemblyName = ARCQuery
BaseTypes = CompoundKey
ClassNamespace = ARCQuery
ClassType = ForeignKey
Description = Can find related values, through compound field names.0x000D0x000A0x000D0x000ALike for 'Order', it can find 'Customer.FirstName' (assuming 'Order' contains 'CustomerId').0x000D0x000ACan relate several steps like for 'OrderLine', 'Order.Customer.FirstName'.0x000D0x000ASee -ToOne-.0x000D0x000A0x000D0x000ACan also traverse 'the other' way  (-ToMany-), like for 'Customer', 'Order.OrderLine.Sum.Sum()' (assuming 'Order' contains 'CustomerId' and 'OrderLine' contains 'OrderId').0x000D0x000A0x000D0x000ANote that in a series of mixed traversal (that is containing both -ToMany- and -ToOne-) each -ToOne- traversal will be limited to distinct primary keys.0x000D0x000AFor instance (from the ARNorthwind example database), for query 'Territory/SELECT EmployeeTerritory.Employee.Order.OrderLine.Sum()' only unique 'EmployeeId' will be used before looking up 'Order'.0x000D0x000A(this does not necessarily make the query above meaningful though).0x000D0x000A0x000D0x000AForeign key can be used in combination with -EntityMethodKey-, -NewKey- and -FunctionKey-.0x000D0x000AFor instance like 'Order/SELECT ShippedDate, Sum, Customer.Name' were 'Customer.Name' is an -EntityMethodKey- combining FirstName, LastName and CompanyName).0x000D0x000A0x000D0x000AThis is an not an expandable concept (class is sealed).0x000D0x000AIn other words, this class contains all the relevant functionality and you are not expected to implement anything specific in your -ApplicationSpecificCode-.0x000D0x000A0x000D0x000ANote: In queries like0x000D0x000A  "Order/SELECT CustomerId, Created, Amount/WHERE Customer.FirstName = 'John'"0x000D0x000Athe foreign-key 'CustomerId' should be included as shown in here (see -QueryExpressionSelect-).0x000D0x000AIf you only do0x000D0x000A  "Order/SELECT Created, Amount/WHERE Customer.FirstName = 'John'"0x000D0x000Athen the link to Customer is not available.0x000D0x000A(For the example given above it would of course have been more natural to just write:0x000D0x000A  "Order/WHERE Customer.FirstName = 'John'/SELECT Created, Amount"0x000D0x000A)0x000D0x000ASee also -MemberEntityKey-.0x000D0x000A0x000D0x000A

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