entc: add option to use entc as package

Summary: Pull Request resolved: https://github.com/facebookincubator/ent/pull/72

Reviewed By: alexsn

Differential Revision: D17783580

fbshipit-source-id: 597f124a28415fef66b0b16811ad2acac8df631d

doc/md/code-gen.md

@@ -9,7 +9,7 @@ title: Introduction
 `entc` run the following command:
 
 ```bash
-go get github.com/facebookincubator/ent/entc/cmd/entc
+go get github.com/facebookincubator/ent/cmd/entc
 ``` 
 
 ## Initialize A New Schema
@@ -33,12 +33,6 @@ the assets for working with your entities. Run the following command:
 entc generate ./ent/schema
 ```
 
-You should note that `goimports` is required for the codegen, and it can be installed using:
-
-```bash
-go get -u golang.org/x/tools/cmd/goimports
-``` 
-
 The `generate` command generates the following assets for the schemas:
 
 - `Client` and `Tx` objects used for interacting with the graph.
@@ -47,6 +41,24 @@ The `generate` command generates the following assets for the schemas:
 - Package containing constants and predicates used for interacting with the builders.
 - A `migrate` package for SQL dialects. See [Migration](migrate.md) for more info.
 
+## Version Compatibility Between `entc` And `ent`
+
+When working with `entc` in a project, you want to make sure that the version being
+used by `entc` is **identical** to the `ent` version used by your project.
+
+One of the options for achieving this is asking `go generate` to use the version
+mentioned in the `go.mod` file when running `entc`. 
+
+Add a `generate.go` file to your project under `<project>/ent`:
+
+```go
+package ent
+
+//go:generate go run github.com/facebookincubator/ent/cmd/entc generate ./schema
+```
+
+And run `go generate ./ent` from your project root directory in order to run `entc` for your project.
+
 ## Code Generation Options
 
 For more info about codegen options, run `entc generate -h`:
@@ -83,6 +95,35 @@ a file with the same name as the template.
 Example of a custom template provides a `Node` API for GraphQL - 
 [Github](https://github.com/facebookincubator/ent/blob/master/entc/integration/template/ent/template/node.tmpl).
 
+## Use `entc` As A Package
+
+Another option for running `entc` is to use it as a package as follows:
+
+```go
+package main
+
+import (
+	"log"
+
+	"github.com/facebookincubator/ent/entc"
+	"github.com/facebookincubator/ent/entc/gen"
+	"github.com/facebookincubator/ent/schema/field"
+)
+
+func main() {
+	err := entc.Generate("./schema", &gen.Config{
+		Header: "// Your Custom Header",
+		IDType: &field.TypeInfo{Type: field.TypeInt},
+	})
+	if err != nil {
+		log.Fatal("running ent codegen:", err)
+	}
+}
+```
+
+The full example exists in [GitHub](https://github.com/facebookincubator/ent/tree/master/examples/entcpkg).
+
+
 ## Schema Description
 
 In order to get a description of your graph schema, run:

doc/md/getting-started.md

@@ -17,7 +17,7 @@ sidebar_label: Quick Introduction
 ## Installation
 
 ```console
-go get github.com/facebookincubator/ent/entc/cmd/entc
+go get github.com/facebookincubator/ent/cmd/entc
 ```
 
 After installing `entc` (the code generator for `ent`), you should have it in your `PATH`.