orm: update readme with more specifics (#21697)

Author: splashsky

vlib/orm/README.md

@@ -1,32 +1,45 @@
 # ORM
 
-## Null
+V has a powerful, concise ORM baked in! Create tables, insert records, manage relationships, all
+regardless of the DB driver you decide to use.
 
-Use option fields in V structs for fields which can be NULL.  Regular,
-non-option fields are defied as NOT NULL when creating tables.
+## Nullable
+
+For a nullable column, use an option field. If the field is non-option, the column will be defined
+with `NOT NULL` at table creation.
+
+```v ignore
+struct Foo {
+    notnull  string
+    nullable ?string
+}
+```
 
 ## Attributes
 
 ### Structs
 
-- `[table: 'name']` sets a custom table name
+- `[table: 'name']` explicitly sets the name of the table for the struct
 
 ### Fields
 
 - `[primary]` sets the field as the primary key
-- `[unique]` sets the field as unique
-- `[unique: 'foo']` adds the field to a unique group
+- `[unique]` gives the field a `UNIQUE` constraint
+- `[unique: 'foo']` adds the field to a `UNIQUE` group
 - `[skip]` or `[sql: '-']` field will be skipped
 - `[sql: type]` where `type` is a V type such as `int` or `f64`
-- `[sql: serial]` lets the DB backend choose a column type for a auto-increment field
+- `[sql: serial]` lets the DB backend choose a column type for an auto-increment field
 - `[sql: 'name']` sets a custom column name for the field
-- `[sql_type: 'SQL TYPE']` sets the sql type which is used in sql
-- `[default: 'raw_sql]` inserts `raw_sql` verbatim in a "DEFAULT" clause when
-  create a new table, allowing for values like `CURRENT_TIME`
+- `[sql_type: 'SQL TYPE']` explicitly sets the type in SQL
+- `[default: 'raw_sql']` inserts `raw_sql` verbatim in a "DEFAULT" clause when
+  creating a new table, allowing for SQL functions like `CURRENT_TIME`. For raw strings, 
+  surround `raw_sql` with backticks (`).
 - `[fkey: 'parent_id']` sets foreign key for an field which holds an array
 
 ## Usage
 
+Here are a couple example structs showing most of the features outlined above.
+
 ```v ignore
 import time
 
@@ -47,23 +60,55 @@ struct Child {
 }
 ```
 
-### Create
+To use the ORM, there is a special interface that lets you use the structs and V itself in queries.
+This interface takes the database instance as an argument.
 
 ```v ignore
+import db.sqlite
+
+db := sqlite.connect(':memory:')!
+
 sql db {
-    create table Foo
+    // query; see below
 }!
 ```
 
-### Drop
+When you need to reference the table, simply pass the struct itself.
 
 ```v ignore
+import models.Foo
+
+struct Bar {
+    id int @[primary; sql: serial]
+}
+
 sql db {
-    drop table Foo
+    create table models.Foo
+    create table Bar
 }!
 ```
 
-### Insert
+### Create & Drop Tables
+
+You can create and drop tables by passing the struct to `create table` and `drop table`.
+
+```v ignore
+import models.Foo
+
+struct Bar {
+    id int @[primary; sql: serial]
+}
+
+sql db {
+    create table models.Foo
+    drop table Bar
+}!
+```
+
+### Insert Records
+
+To insert a record, create a struct and pass the variable to the query. Again, reference the struct
+as the table.
 
 ```v ignore
 foo := Foo{
@@ -86,52 +131,76 @@ foo_id := sql db {
 }!
 ```
 
-If the `id` field is marked as `serial` and `primary`, the insert expression
+If the `id` field is marked as `sql: serial` and `primary`, the insert expression
 returns the database ID of the newly added object. Getting an ID of a newly
 added DB row is often useful.
 
 When inserting, `[sql: serial]` fields, and fields with a `[default: 'raw_sql']`
-attribute are not sent to the database when the value being sent is the default
+attribute, are not sent to the database when the value being sent is the default
 for the V struct field (e.g., 0 int, or an empty string).  This allows the
 database to insert default values for auto-increment fields and where you have
 specified a default.
 
+### Select
 
-### Update
+You can select rows from the database by passing the struct as the table, and
+use V syntax and functions for expressions. Selecting returns an array of the
+results.
 
 ```v ignore
-sql db {
-    update Foo set updated_at = time.now() where name == 'abc' && updated_at is none
+result := sql db {
+    select from Foo where id == 1
 }!
-```
 
-Note that `is none` and `!is none` can be used to select for NULL fields.
+foo := result.first()
+```
 
-### Delete
 ```v ignore
-sql db {
-    delete from Foo where id > 10
+result := sql db {
+    select from Foo where id > 1 && name != 'lasanha' limit 5
 }!
 ```
 
-### Select
 ```v ignore
 result := sql db {
-    select from Foo where id == 1
+    select from Foo where id > 1 order by id
 }!
 ```
+
+
+### Update
+
+You can update fields in a row using V syntax and functions. Again, pass the struct
+as the table.
+
 ```v ignore
-result := sql db {
-    select from Foo where id > 1 && name != 'lasanha' limit 5
+sql db {
+    update Foo set updated_at = time.now() where name == 'abc' && updated_at is none
 }!
 ```
+
+Note that `is none` and `!is none` can be used to select for NULL fields.
+
+### Delete
+
+You can delete rows using V syntax and functions. Again, pass the struct
+as the table.
+
 ```v ignore
-result := sql db {
-    select from Foo where id > 1 order by id
+sql db {
+    delete from Foo where id > 10
 }!
 ```
 
-### Example
+### time.Time Fields
+
+It's definitely useful to cast a field as `time.Time` so you can use V's built-in time functions;
+however, this is handled a bit differently than expected in the ORM. `time.Time` fields are 
+created as integer columns in the database. Because of this, the usual time functions 
+(`current_timestamp`, `NOW()`, etc) in SQL do not work as defaults.
+
+## Example
+
 ```v ignore
 import db.pg