| | 1 | ---- |
| | 2 | = FDO RFC 69 - Enhanced OGR Provider = |
| | 3 | |
| | 4 | This page contains a request for comments document (RFC) for the FDO Open Source project. |
| | 5 | More FDO RFCs can be found on the [wiki:FDORfcs RFCs] page. |
| | 6 | |
| | 7 | == Status == |
| | 8 | |
| | 9 | ||RFC Template Version||(1.1)|| |
| | 10 | ||Submission Date||12 August 2014|| |
| | 11 | ||Last Modified||12 August 2014|| |
| | 12 | ||Author||Jackie Ng|| |
| | 13 | ||RFC Status||draft|| |
| | 14 | ||Implementation Status||in progress|| |
| | 15 | ||Proposed Milestone||FDO vNext|| |
| | 16 | ||Assigned PSC guide(s)|||| |
| | 17 | ||'''Voting History'''|| || |
| | 18 | ||+1|| || |
| | 19 | ||+0|| || |
| | 20 | ||-0|| || |
| | 21 | ||-1|| || |
| | 22 | |
| | 23 | == Overview == |
| | 24 | |
| | 25 | This RFC is for enhancing the capabilities of the OGR provider and improving its reliability |
| | 26 | |
| | 27 | == Motivation == |
| | 28 | |
| | 29 | The OGR provider is very barebones in terms of FDO capabilities, this makes it difficult to author layers from OGR Feature Sources in MapGuide as we can only render/stylize from OGR feature attributes as-is as the provider lacks support for FDO expression functions that let us format/shape this data during layer stylization. |
| | 30 | |
| | 31 | Also the OGR provider lacks a basic unit test suite, which gives us no objective baseline as to the reliability of this particular provider. |
| | 32 | |
| | 33 | == Proposed Solution == |
| | 34 | |
| | 35 | The OGR provider will be enhanced with FDO Expression Engine support. The OGR expression capabilities will now return the full suite of functions supported by the FDO Expression Engine. |
| | 36 | |
| | 37 | The Expression Engine will be used for both Select and SelectAggregates commands. However, use of the Expression Engine will only happen outside of the following cases: |
| | 38 | |
| | 39 | * SelectAggregates with single property or aggregate function and no FDO Filter |
| | 40 | * `Count()` will internally issue the following OGR SQL: `SELECT count_expr FROM feature_class` |
| | 41 | * `SpatialExtents()` will internally use `OGRLayer::GetExtent()`. Where supported, fast extent (`bForce = FALSE`) is used. Otherwise we brute force (`bForce = TRUE`) |
| | 42 | * Single property with distinct = true will internally issue the following OGR SQL: `SELECT DISTINCT prop_name FROM feature_class` |
| | 43 | * Select |
| | 44 | * Expression Engine will not be invoked if the select command has no computed identifiers |
| | 45 | |
| | 46 | This RFC will also fix some defects in the provider that either already existed or were discovered during the implementation of this RFC: |
| | 47 | |
| | 48 | * #885: Use fast extent where possible for `FdoISpatialContextReader::GetExtent()` |
| | 49 | * `FdoIConnection::Open()` should fail if `DataStore` property is not specified |
| | 50 | * Executing any FDO Command should fail if connection is not open |
| | 51 | * OGRLayer pointers do not have their internal iterators reset before select/insert/update/delete, causing potential inconsistent results when executing multiple FDO select/insert/update/delete commands in succession on the same connection |
| | 52 | |
| | 53 | We will also implement a basic unit test suite for the OGR provider to exercise Expression Engine support and key provider functionalities. |
| | 54 | |
| | 55 | == Test Plan == |
| | 56 | |
| | 57 | Ensure the new test suite passes on both Windows and Linux. |
| | 58 | |
| | 59 | == !Funding/Resources == |
| | 60 | |
| | 61 | Community |
