Add support for type converters

[vitusortner]

The long-awaited type converters are here! 🎉

Public API

First, some words about the public API of type converters. I wanted to make type converters as safe as possible at compile time. Thereby, I added an abstract TypeConverter class that required two type parameters. The first is the encoded type that is used outside of the database scope. The second type is the decoded database type. The abstract class, furthermore, comes with the two functions encode() and decode() which have to be overridden by the implementation classes. This way, we can be sure that there always is functionality provided for conversion in both directions. Room is missing this extra security as they use plain functions as type converters.

A simple type converter that converts from DateTime to int and vice versa is shown in the following.

class DateTimeConverter extends TypeConverter<DateTime, int> {
  @override
  DateTime decode(int databaseValue) {
    return DateTime.fromMillisecondsSinceEpoch(databaseValue);
  }

  @override
  int encode(DateTime value) {
    return value.millisecondsSinceEpoch;
  }
}

Such a class can then be applied to the database with different scope restrictions by using the @TypeConverters annotation. These scopes are:

1. databases
2. DAOs
3. entities/views
4. entity/view fields
5. DAO methods
6. DAO method parameters

Implementation

Floor generates and uses type converter as described in the following.

Processors

1. Collect type converters with the database scope and pass these to all processors
2. Collect type converters with the DAO scope and pass these to the specific DAO processor
3. This basically happens for each scope level and thereby, the processors only get the relevant type converters

Writers

1. Instantiate/write an object of each type converter class it can find (it has to be added with @TypeConverters)
2. Use the generated type converters throughout the generated code when needed

This still needs work:

• tests (validate type converter scopes/order and correct usage)

Closes #165
Closes #313 as we won't fall back to double when the type of a field is unknown

[codecov]

Codecov Report

Merging #318 into develop will increase coverage by 1.14%.
The diff coverage is 83.01%.

@@             Coverage Diff             @@
##           develop     #318      +/-   ##
===========================================
+ Coverage    81.56%   82.71%   +1.14%     
===========================================
  Files           60       68       +8     
  Lines         1535     1660     +125     
===========================================
+ Hits          1252     1373     +121     
- Misses         283      287       +4     

Flag	Coverage Δ
#floor	82.71% <83.01%> (+1.14%)	⬆️
#floor_generator	82.50% <83.01%> (+1.34%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...loor_generator/lib/value_object/change_method.dart	15.78% <ø> (+1.50%)	⬆️
floor_generator/lib/value_object/dao.dart	3.70% <0.00%> (-0.30%)	⬇️
floor_generator/lib/value_object/database.dart	10.34% <0.00%> (-1.66%)	⬇️
...or_generator/lib/value_object/deletion_method.dart	50.00% <0.00%> (-50.00%)	⬇️
...r_generator/lib/value_object/insertion_method.dart	18.18% <0.00%> (ø)
floor_generator/lib/value_object/field.dart	64.00% <40.00%> (-1.22%)	⬇️
floor_generator/lib/value_object/query_method.dart	63.33% <50.00%> (-0.96%)	⬇️
floor_generator/lib/processor/field_processor.dart	89.18% <77.77%> (-0.47%)	⬇️
floor_generator/lib/value_object/entity.dart	95.12% <87.50%> (-1.11%)	⬇️
...loor_generator/lib/writer/query_method_writer.dart	97.43% <88.88%> (-2.57%)	⬇️
... and 27 more

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[fnicastri]

@mqus
Thanks for your time, it was just an idea.
@avbk
Yu can definitely merge Recipe and RecipeDTO, the only downside is when you have a lot of annotations, it starts to feel messy

[fingerart]

@vitusortner
Hi. Do you have an approximate release date for this feature?

[FlashLight13]

@vitusortner Hi! Any updates on this? 🙂

[vitusortner]

I finally have some more time to look into this feature again. I'll keep you updated!