ent/doc: add crud code examples to doc

Reviewed By: alexsn

Differential Revision: D17110486

fbshipit-source-id: 5575b9f63769744bf2fe5f8f27f83ab6446db6e5

doc/md/crud.md

@@ -95,12 +95,137 @@ func main() {
 
 ## Create An Entity
 
-## Update An Entity
+**Save** a user.
 
-## Update Many Entities
+```go
+a8m, err := client.User.	// UserClient.
+	Create().				// User create builder.
+	SetName("a8m").			// Set field value.
+	SetNillableAge(age).	// Avoid nil checks.
+	AddGroups(g1, g2).		// Add many edges.
+	SetSpouse(nati).		// Set unique edge.
+	Save(ctx)				// Create and return.
+```
 
-## Query An Entity
+**SaveX** a user; Unlike **Save**, **SaveX** panics if an error occurs.
 
-## Delete An Entity
+```go
+pedro := client.Pet.	// PetClient.
+	Create().			// User create builder.
+	SetName("pedro").	// Set field value.
+	SetOwner(a8m).		// Set owner (unique edge).
+	SaveX(ctx)			// Create and return.
+```
 
-## Delete Entities
+## Update One
+
+If an entity that already returned from the database.
+
+```go
+a8m, err = a8m.Update().	// User update builder.
+	RemoveGroup(g2).		// Remove specific edge.
+	ClearCard().			// Clear unique edge.
+	SetAge(30).				// Set field value
+	Save(ctx)				// Save and return.
+```
+
+
+## Update By ID
+
+```go
+pedro, err := client.Pet.	// PetClient.
+	UpdateOneID(id).		// Pet update builder.
+	SetName("pedro").		// Set field name.
+	SetOwnerID(owner).		// Set unique edge, using id.
+	Save(ctx)				// Save and return.
+```
+
+## Update Many
+
+Filter using predicates.
+
+```go
+n, err := client.User.			// UserClient.
+	Update().					// Pet update builder.
+	Where(						//
+		user.Or(				// (age >= 30 OR name = "bar") 
+			user.AgeEQ(30), 	//
+			user.Name("bar"),	// AND
+		),						//  
+		user.HasFollowers(),	// UserHasFollowers()  
+	).							//
+	SetName("foo").				// Set field name.
+	Save(ctx)					// exec and return.
+```
+
+Query edge-predicates.
+
+```go
+n, err := client.User.			// UserClient.
+	Update().					// Pet update builder.
+	Where(						// 
+		user.HasFriendsWith(	// UserHasFriendsWith (
+			user.Or(			//   age = 20
+				user.Age(20),	//      OR
+				user.Age(30),	//   age = 30
+			)					// )
+		), 						//
+	).							//
+	SetName("a8m").				// Set field name.
+	Save(ctx)					// exec and return.
+```
+
+## Query The Graph
+
+Get all users with followers.
+```go
+users, err := client.User.		// UserClient.
+	Query().					// User query builder.
+	Where(user.HasFollowers()).	// filter only users with followers.
+	All(ctx)					// query and return.
+```
+
+Get all followers of a specific user; Start the traversal from a node in the graph.
+```go
+users, err := a8m.
+	QueryFollowers().
+	All(ctx)
+```
+
+Get all pets of the followers of a user.
+```go
+users, err := a8m.
+	QueryFollowers().
+	QueryPets().
+	All(ctx)
+```
+More advance traversals can be found in the [next section](traversals.md). 
+
+## Delete One 
+
+Delete an entity.
+
+```go
+err := client.User.
+	DeleteOne(a8m).
+	Exec(ctx)
+```
+
+Delete by id.
+
+```go
+err := client.User.
+	DeleteOneID(id).
+	Exec(ctx)
+```
+
+## Delete Many
+
+Delete using predicates.
+
+```go
+err := client.File.
+	Delete().
+	Where(file.UpdatedAtLT(date))
+	Exec(ctx)
+```