Add mods to fields, specifically for "lower(field)" in SQL

[peterbroadhurst]

Have a microservice with a requirement to use lower(address) function on query filters against the DB, in order to work with a PostgreSQL index on lower(address). This allows efficient indexed query, using case insensitive searches (for example using the checksumed Eth address).

With this PR, it should be as simple as:

firefly-common/pkg/dbsql/filter_sql_test.go

Line 43 in 8c28b1d

"address": &ffapi.StringFieldLower{},

[codecov-commenter]

Codecov Report

Merging #92 (8c28b1d) into main (992357b) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main       #92   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           63        63           
  Lines         4885      4905   +20     
=========================================
+ Hits          4885      4905   +20     

Files Changed	Coverage Δ
pkg/dbsql/filter_sql.go	100.00% <100.00%> (ø)
pkg/ffapi/filter.go	100.00% <100.00%> (ø)
pkg/ffapi/query_fields.go	100.00% <100.00%> (ø)

[nguyer]

Looks good! It did take me a minute to figure out that fmt.Sprintf("lower(%s)", fieldName) was not a way for Go to lowercase the string, but for the DB to lowercase the string 🙃 Need more coffee still.