Rails is easy with database nullable fields, it return a nil if the column value is NULL. It's idiomatic and transparent for us developers.

But Go is a strict typed language, if you set a struct attribute as string, then you can't evaluate it as nil. Here's is a post for the situation: working-with-db-nulls.

Go hasn't a nil for its basic types, but it provides zero values for them:

string: "" int: 0 bool: false float: 0.0 time.Time: '0001-01-01 00:00:00','+00:00','UTC' 

So for the database nullable field, if a string typed field value is NULL, we can set it as "" to make it consistent with Go's zero value specification.

I hope go-on-rails can work with the nullable fields like Rails does, so I searched the web and found the COALESCE, a function available in most popular databases, here is the spark of inspiration: https://github.com/go-sql-driver/mysql/issues/34#issuecomment-158391340.

Its basic usage is like this:

 COALESCE(column_a, [column_b, "default_string"]) AS an_alias_for_column_a

Here it means that if column_a is NULL, we return one of its parameter in turn from the second ones which maybe is a column_b for query or simply a same typed value for return.

So we can take the zero values for the COALESCE's second parameter, it'll be returned if the nullable field is NULL.

That's it!

Then go-on-rails v0.1.11 is released with the feature built in. All the functions generated by go-on-rails with a SELECT query is enhanced with the COALESCE.

And I write a Go package as a helper for you to write your own SQL clause that's also safe with nullable fields: zero.

For example, we has a struct:

type Person struct { Name string // Not NULL Age int // Nullable field in database  Address // Nullable field in database }

we write a select clause for it with zero and then use the go-on-rails generated FindPersonsBySql() function to execute the query:

import ( "fmt" "github.com/railstack/zero" // here we import the models in a relative path,  // we assume it is in the up folder of the current "controllers" folder  m "../models" ) sql := fmt.Sprintf("SELECT id, name, %v, %v FROM persons", zero.Int("age"), zero.String("address")) ps, err := m.FindPersonsBySql(sql) if err != nil { /* ... */ } fmt.Printf("Persons: %+v", ps)