Create an Oracle dialect

[jimlambrt]

Make sure these boxes checked before submitting your pull request.

• Do only one thing
• No API-breaking changes
• New code/logic commented & tested

For significant changes like big bug fixes, new features, please open an issue to make an agreement on an implementation design/plan first before starting it.

What did this pull request do?

Implement support for oracle and an oracle dialect: oci8.

Why add an oracle dialect directly to gorm, instead of just writing one in a separate repo?
There are several parts of scope.go that include incompatible SQL, and gorm currently doesn't support overriding those behaviors, so a few judicious changes were needed, which were all prefaced with a call to scope.IsOra() to isolate them from the rest of the implementation

This PR includes:

• Define an OraCommon type which implements all the common behaviors for Oracle across drivers. Please see dialect_oracommon.go where you'll find documentation for many of the design/implementation choices and why they were made.
• Define an OraDialect interface so other oracle drivers can override behavior around "last insert id" and make it easy to assert that a dialect implements oracle
• Define a new dialect "oci8" that uses the driver github.com/mattn/go-oci8 I've also included a README that documents how-to install the driver and its dependencies along with Oracle for testing.
• All existing unit tests pass. This required cleaning up some trailing semicolons in existing tests and adding a few oracle specific cases to handle how oracle deals with identifiers (quoting and upper casing). These changes are all prefaced by a call to the isOra() func.

Thank you for you careful consideration of this PR. -Jim

[codecov-io]

Codecov Report

Merging #2891 into master will increase coverage by 0.49%.
The diff coverage is 80.69%.

@@            Coverage Diff             @@
##           master    #2891      +/-   ##
==========================================
+ Coverage   79.01%   79.50%   +0.49%     
==========================================
  Files          24       25       +1     
  Lines        3540     3737     +197     
==========================================
+ Hits         2797     2971     +174     
- Misses        642      659      +17     
- Partials      101      107       +6     

Impacted Files	Coverage Δ
scope.go	87.06% <70.00%> (+0.02%)	⬆️
dialect_oracommon.go	82.24% <82.24%> (ø)
callback_create.go	86.66% <100.00%> (+0.34%)	⬆️
callback_query_preload.go	87.50% <0.00%> (-1.25%)	⬇️
association.go	93.27% <0.00%> (+0.89%)	⬆️
main.go	82.02% <0.00%> (+0.92%)	⬆️
callback_query.go	86.20% <0.00%> (+3.44%)	⬆️
utils.go	89.56% <0.00%> (+4.34%)	⬆️

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[jimlambrt]

Getting close on the wercker builds. I had to run the code coverage test twice and merge it with github.com/wadey/gocovmerge since the default just runs the sqlite tests and reports 0% coverage on my new common ora dialect. At the moment, the mariadb container is failing to start, which isn't something I changed... hum. Re-running local tests, after deleting all my local docker containers/vols to see if I can reproduce the issue.

BTW, running oracle in a container is a dumpster fire no doubt. I used the official docker repo for building it: https://github.com/oracle/docker-images. Wow, it's a big container and takes forever to start up.

[nlamot]

Hi @jimlambrt, this looks great! Is there any news on when this will be merged to master?
We would like to use GORM as well to connect to an Oracle DB.

[jimlambrt]

@nlamot At this point, I think we're waiting for v2 before anything gets merged... and I'm not sure what that means for this new dialect.

[jimlambrt]

Well, looks like the latest mysql image (3 days ago) broke the automated wercker tests for mysql

[FlyingOnion]

I think that it is better to remove specific database judging. It should be implemented separately (I know oracle is very different).

[jinzhu]

The PR is closed due to it is developed based on V1, I’d really appreciate it if someone would like to develop it based on V2.

[jinzhu]

@jimlambrt let me know if you would like to create a repo on https://github.com/go-gorm, thank you.