Add a new sub-operation to the 'alter column' operation to drop `NOT
NULL` constraints from columns.
Currently, it is only possible to **set** `NOT NULL` constraints on
columns but not remove them. The syntax for doing this is:
```json
{
"name": "16_set_nullable",
"operations": [
{
"alter_column": {
"table": "reviews",
"column": "review",
"nullable": false,
"up": "(SELECT CASE WHEN review IS NULL THEN product || ' is good' ELSE review END)",
"down": "review"
}
}
]
}
```
Setting `nullable: true` in the above migration would result in a
validation error saying that removing `NOT NULL` constraints was not
supported. This PR removes this restriction and allows `nullable: true`
to remove an existing `NOT NULL` constraint.
A migration to remove a `NOT NULL` constraint looks like:
```json
{
"name": "31_unset_not_null",
"operations": [
{
"alter_column": {
"table": "posts",
"column": "title",
"nullable": true,
"up": "title",
"down": "(SELECT CASE WHEN title IS NULL THEN 'placeholder title' ELSE title END)"
}
}
]
}
```
The differences between adding and removing a `NOT NULL` constraint are:
* `nullable: true` vs `nullable: false`
* The roles of `up` and `down` SQL are reversed; `down` now needs to
rewrite any `NULL`s to meet the `NOT NULL` constraint on the old column.
`up` defaults to a simple copy of the data from the old column to the
new.
Fixes#223
Update the **create table** and **add column** operations so that they
support adding [Postgres
comments](https://www.postgresql.org/docs/current/sql-comment.html):
* **create table**: comments can be added to the table itself and to
each of its columns.
* **add column**: a comment can be added to the column.
A **create table** migration that includes a comment on the table itself
and on one of its columns looks like this:
```json
{
"name": "12_create_employees_table",
"operations": [
{
"create_table": {
"name": "employees",
"comment": "This is a comment for the employees table",
"columns": [
{
"name": "id",
"type": "serial",
"pk": true
},
{
"name": "role",
"type": "varchar(255)",
"comment": "This is a comment for the role column"
}
]
}
}
]
}
```
and an **add column** migration that includes a comment looks like this:
```json
{
"name": "30_add_column_simple_up",
"operations": [
{
"add_column": {
"table": "people",
"up": "'temporary-description'",
"column": {
"name": "description",
"type": "varchar(255)",
"nullable": false,
"comment": "This is a comment for the description column"
}
}
}
]
}
```
This allows new tables and columns to be created with comments.
Deletion and modification of comments should still be performed with a
raw SQL migration. Until we see a use case that requires versioned
modification/removal of comments, these operations are best performed
directly on the base table with raw SQL.
All structs matched well except for `PrimaryKey` which we mapped
differently, I've refactored it to `Pk` as it doesn't seem to support
different names for go and JSON
---------
Signed-off-by: Alexis Rico <sferadev@gmail.com>
Co-authored-by: Andrew Farries <andyrb@gmail.com>
