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Description

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= Represents part of a query (or actually a transformation) against a given collection and the data storage from which it was taken.0x000D0x000A0x000D0x000AA series of queries are usually chained together in a fluent fashion0x000D0x000Afor instance as an API call like:0x000D0x000A  'api/RQ/Order/WHERE Value 0x003E 1000 NOK/REL Customer/ORDER BY LastName, FirstName/TAKE 50/'0x000D0x000Aor as a C# expression like:0x000D0x000A  'new QueryProgress(DataStorage, Orders).Where("Value 0x003E 100").Rel(typeof(Customer)).OrderBy("LastName,FirstName").Take(50)'0x000D0x000A(but in the latter case the standard LINQ extension in .NET will of course usually provide the same or better functionality (expect for AgoRapide unique queries like -QueryExpressionRel-)).0x000D0x000A0x000D0x000ASee also -CompoundKey- which expands the concept of keys.0x000D0x000A0x000D0x000AThe main purpose of the -QueryExpression- concept is to empower API users to create their own simple ad-hoc reports, without needing assistance from the API developers (that is, without any C# code having to be written or new API endpoints to be created).0x000D0x000A0x000D0x000AThe -QueryExpression- concept is not meant to be exhaustive with relation to relational modelling, nor is it proven formally.0x000D0x000AThis concept just takes away some (or actually rather quite a lot) of the need for 'hand-crafted' code in order to cover what are quite often very common scenarios.0x000D0x000A0x000D0x000AMore complex needs can be covered by -ApplicationSpecificCode- implementations of this class (see below).0x000D0x000A0x000D0x000ANote that queries can also be embedded in a -Subscription- (but this only gives meaning when querying against a hierarchical object storage, see -AdHocQuery-).0x000D0x000A0x000D0x000AThe most important implementing classes in -StandardAgoRapideCode- are:0x000D0x000A-QueryExpressionAll-0x000D0x000A-QueryExpressionSelect-0x000D0x000A-QueryExpressionWhere-0x000D0x000A-QueryExpressionOrderBy-0x000D0x000A-QueryExpressionSkip-0x000D0x000A-QueryExpressionTake-0x000D0x000ASome classes useful for aggregation queries are:0x000D0x000A-QueryExpressionPivot-0x000D0x000A-QueryExpressionAggregate-0x000D0x000A-QueryExpressionRel-0x000D0x000ASelf creation of collection:0x000D0x000A-QueryExpressionSelfCreate-0x000D0x000AOther implementing classes:0x000D0x000A-QueryExpressionDataStorage-0x000D0x000A-QueryExpressionTitle-0x000D0x000A-QueryExpressionShuffle-0x000D0x000A-QueryExpressionLimit-0x000D0x000A-QueryExpressionHint-0x000D0x000A-QueryExpressionStrict-0x000D0x000A-QueryExpressionCache-0x000D0x000A-QueryExpressionComment-0x000D0x000A0x000D0x000ATODO: Potential sub-classes to be added:0x000D0x000A-QueryExpressionUnion- (for instance like /UNION 0x007BsubQuery0x007D)0x000D0x000A0x000D0x000ANote that the concept is inherently expandable, you can create your own sub-classes and integrate them with -StandardAgoRapideCode-.0x000D0x000ANote how any -ApplicationSpecificCode- implementations must be added to -Parsers- at application startup in order for them to be recognized by -TryParse-.0x000D0x000A0x000D0x000AOne practical application for -ApplicationSpecificCode- implementations of -QueryExpression- is hand-crafted reports, for instance a 'QueryExpressionReport042', available as for instance 'api/RQ/Report042'.0x000D0x000AAnother application could be hand-crafted HTML-representations of result sets.0x000D0x000A0x000D0x000ASee also -CompoundKey- (like -ForeignKey-, -EntityMethodKey- and -NewKey-),0x000D0x000A-FunctionKey-,0x000D0x000A-QuantileKey- and0x000D0x000A-ValueComparer-.0x000D0x000A0x000D0x000AThe implementations of -QueryExpression- (together with the classes mentioned above) constitute building blocks which for instance an API end-user can fit together to construct reports as needed.0x000D0x000AThis compares well to monolithic report creation where elements can not be reused easily.0x000D0x000A(it is similar to the UNIX philosophy of small utilities each performing a well defined easy-to-understand function).0x000D0x000A0x000D0x000ASome online applications demonstrating -QueryExpression- are:0x000D0x000Ahttp://ARNorthwind.AgoRapide.com and0x000D0x000Ahttp://ARAdventureWorksOLAP.AgoRapide.com 0x000D0x000A

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