Add default value expression option

bq_field.proto

@@ -44,6 +44,12 @@ message BigQueryFieldOptions {
 
   // Optionally add PolicyTag for a field in BigQuery schema.
   string policy_tags = 6;
+
+  // Optional default value.
+  //
+  // See https://cloud.google.com/bigquery/docs/default-values for possible
+  // values.
+  string default_value_expression = 7;
 }
 
 

go.mod

@@ -3,6 +3,6 @@ module github.com/GoogleCloudPlatform/protoc-gen-bq-schema
 go 1.16
 
 require (
-	github.com/golang/glog v1.2.0
+	github.com/golang/glog v1.2.1
 	google.golang.org/protobuf v1.33.0
 )

go.sum

@@ -1,5 +1,7 @@
 github.com/golang/glog v1.2.0 h1:uCdmnmatrKCgMBlM4rMuJZWOkPDqdbZPnrMXDY4gI68=
 github.com/golang/glog v1.2.0/go.mod h1:6AhwSGph0fcJtXVM/PEHPqZlFeoLxhs7/t5UDAwmO+w=
+github.com/golang/glog v1.2.1 h1:OptwRhECazUx5ix5TTWC3EZhsZEHWcYWY4FQHTIubm4=
+github.com/golang/glog v1.2.1/go.mod h1:6AhwSGph0fcJtXVM/PEHPqZlFeoLxhs7/t5UDAwmO+w=
 github.com/golang/protobuf v1.5.0/go.mod h1:FsONVRAS9T7sI+LIUmWTfcYkHO4aIWwzhcaSAoJOfIk=
 github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
 github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=

pkg/converter/convert.go

@@ -64,12 +64,13 @@ var (
 
 // Field describes the schema of a field in BigQuery.
 type Field struct {
-	Name        string      `json:"name"`
-	Type        string      `json:"type"`
-	Mode        string      `json:"mode"`
-	Description string      `json:"description,omitempty"`
-	Fields      []*Field    `json:"fields,omitempty"`
-	PolicyTags  *PolicyTags `json:"policyTags,omitempty"`
+	Name                   string      `json:"name"`
+	Type                   string      `json:"type"`
+	Mode                   string      `json:"mode"`
+	Description            string      `json:"description,omitempty"`
+	Fields                 []*Field    `json:"fields,omitempty"`
+	PolicyTags             *PolicyTags `json:"policyTags,omitempty"`
+	DefaultValueExpression string      `json:"defaultValueExpression,omitempty"`
 }
 
 // PolicyTags describes the structure of a Policy Tag
@@ -166,6 +167,10 @@ func convertField(
 				Names: []string{opt.PolicyTags},
 			}
 		}
+
+		if len(opt.DefaultValueExpression) > 0 {
+			field.DefaultValueExpression = opt.DefaultValueExpression
+		}
 	}
 
 	if len(field.Description) > 1024 {