[#180] Add a JsonCodec

[lukaseder]

Issue description

Fixes #180

New Public APIs

None

[martypitt]

Would love to see this merged and released, as it's blocking us. In the mean time, I'll use the excellent examples here to work-around. Thanks to @lukaseder for this!

[gregturn]

Thanks @lukaseder.

If you could give the snapshots a spin @martypitt, let us know if you see any issues.

[cbrunsdon]

@gregturn I pulled down the snapshot and ran into problems.

JsonCodec extends AbstractCodec<String>, which means the canEncode call here will return true for any strings passed in.

This causes issues when calling .bind with a string parameter.

Since the JsonCodec is earlier in the list of DefaultCodecs, it will be the first one picked up here causing a DbException when the JsonCodec can't encode a non-json string.

You end up with a stack trace of something like:

 Data conversion error converting "MyString" [22018-200]
org.h2.message.DbException: Data conversion error converting "MyString" [22018-200]
	at org.h2.message.DbException.get(DbException.java:205)
	at org.h2.message.DbException.get(DbException.java:181)
	at org.h2.value.ValueJson.fromJson(ValueJson.java:161)
	at io.r2dbc.h2.codecs.JsonCodec.doEncode(JsonCodec.java:41)
	at io.r2dbc.h2.codecs.JsonCodec.doEncode(JsonCodec.java:23)
	at io.r2dbc.h2.codecs.AbstractCodec.encode(AbstractCodec.java:68)
	at io.r2dbc.h2.codecs.DefaultCodecs.encode(DefaultCodecs.java:70)
	at io.r2dbc.h2.H2Statement.addIndex(H2Statement.java:130)
	at io.r2dbc.h2.H2Statement.bind(H2Statement.java:75)
	at io.r2dbc.h2.H2Statement.bind(H2Statement.java:39)

[lukaseder]

Since the JsonCodec is earlier in the list of DefaultCodecs, it will be the first one picked up here causing a DbException when the JsonCodec can't encode a non-json string.

Ah, nice catch. Did I overlook something, or do the tests not catch this problem?

[dragneelfps]

Hi @lukaseder , any idea when this might be released on maven central?

[lukaseder]

Hi @lukaseder , any idea when this might be released on maven central?

Nope. For I am not in charge here ;-)

[dragneelfps]

So I tried using io.r2dbc:r2dbc-h2:0.9.0.BUILD-SNAPSHOT and it fails to encode varchar(in database) into string(in entity class), since JsonCodec tries to encode before StringCodec.

[cbrunsdon]

Since the JsonCodec is earlier in the list of DefaultCodecs, it will be the first one picked up here causing a DbException when the JsonCodec can't encode a non-json string.

Ah, nice catch. Did I overlook something, or do the tests not catch this problem?

The test's don't catch the problem. From what I can tell, nothing in DefaultCodecs (or anything else) does a test of string conversion with all the default codecs loaded. Not 100% sure this is the right test for it, but threw up a commit with a test that exposes the problem:

cbrunsdon@0d644c1

[dragneelfps]

Let me know, if you don't mind if I create a PR for the fix. Created a bug issue: #195

[jkamcc]

Hello, this PR would be also good to be merged to 0.8.x branch, due that 0.9.x changes are used by an spi and r2dbc version currently (March, 22) that is only supported by a spring boot data r2dbc version not compatible with current stable release of spring boot 2.6.x, and only with 2.7.x which is in M3 stage and not released yet to a stable version.