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Updates flag-gated migration docs (#2186) 

Updates the `isWizard` flag gated migration docs to reflect lessons learned writing #2177 in the described style.
This commit is contained in:
Daniel McCarney 2016-09-19 14:48:10 -04:00 committed by Jacob Hoffman-Andrews
parent 2c966c61b2
commit 46bda771d4
1 changed files with 33 additions and 9 deletions
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42
CONTRIBUTING.md
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@ -78,8 +78,10 @@ Boulder attempts to write that struct to a table that doesn't yet have the
corresponding column (case 1), gorp wil fail with
`Insert failed table posts has no column named Foo`.
There are examples of such models in sa/model.go, along with code to
turn a model into a `struct` used internally. An example of a flag-gated
migration, adding a new `IsWizard` field to Person:
turn a model into a `struct` used internally.
An example of a flag-gated migration, adding a new `IsWizard` field to Person
controlled by a `allowWizards` flag:
```
struct Person {
@ -87,18 +89,20 @@ struct Person {
IsWizard bool // Added!
}
var allowWizards bool // Added!
struct personModelv1 {
HatSize int
}
// Added!
struct personModelv2 {
HatSize int
*personModelv1
IsWizard bool
}
func (ssa *SQLStorageAuthority) GetPerson() (Person, error) {
if ssa.allowWizards { // Added!
if allowWizards { // Added!
var model personModelv2
ssa.dbMap.SelectOne(&model, "SELECT hatSize, isWizard FROM people")
return Person{
@ -110,15 +114,16 @@ func (ssa *SQLStorageAuthority) GetPerson() (Person, error) {
ssa.dbMap.SelectOne(&model, "SELECT hatSize FROM people")
return Person{
HatSize: model.HatSize,
IsWizard: false,
}
}
}
func (ssa *SQLStorageAuthority) AddPerson(p Person) (error) {
if ssa.allowWizards { // Added!
if allowWizards { // Added!
return ssa.dbMap.Insert(personModelv2{
HatSize: p.HatSize,
personModelv1: {
HatSize: p.HatSize,
},
IsWizard: p.IsWizard,
})
} else {
@ -130,11 +135,30 @@ func (ssa *SQLStorageAuthority) AddPerson(p Person) (error) {
}
```
Add a migration with
You will also need to update the `initTables` function from `sa/database.go` to
tell Gorp which table to use for your versioned model structs. Make sure to
consult the flag you defined so that only **one** of the table maps is added at
any given time, otherwise Gorp will error. Depending on your table you may also
need to add `SetKeys` and `SetVersionCol` entries for your versioned models.
Example:
```
func initTables(dbMap *gorp.DbMap) {
// < unrelated lines snipped for brevity >
if allowWizards {
dbMap.AddTableWithName(personModelv2, "person")
} else {
dbMap.AddTableWithName(personModelv1, "person")
}
}
```
You can then add a migration with:
`$ goose -path ./sa/_db/ create AddWizards sql`
Then edit the resulting file (`sa/_db/20160915101011_WizardMigrations.sql`) to add:
Finally, edit the resulting file (`sa/_db/20160915101011_WizardMigrations.sql`) to define your migration:
```
-- +goose Up