Add example of custom numeric type

The main trick is to specify the override on NewQuerierConfig and not on
ConnInfo.RegisterDataType. We can't easily get the data types for pgxpool.Pool
because we need to get a real *Conn which then fetches a connection from the
 pool.

Partially resolves #39.

example/acceptance_test.go

@@ -175,6 +175,14 @@ func TestExamples(t *testing.T) {
 				"--go-type", "text=string",
 			},
 		},
+		{
+			name: "example/numeric_external",
+			args: []string{
+				"--schema-glob", "example/numeric_external/schema.sql",
+				"--query-glob", "example/numeric_external/query.sql",
+				"--go-type", "numeric=github.com/shopspring/decimal.Decimal",
+			},
+		},
 		{
 			name: "example/domain",
 			args: []string{

example/numeric_external/codegen_test.go

@@ -0,0 +1,50 @@
+package numeric_external
+
+import (
+	"github.com/jschaf/pggen"
+	"github.com/jschaf/pggen/internal/pgtest"
+	"github.com/stretchr/testify/assert"
+	"io/ioutil"
+	"path/filepath"
+	"testing"
+)
+
+func TestGenerate_Go_Example_Numeric_External(t *testing.T) {
+	conn, cleanupFunc := pgtest.NewPostgresSchema(t, []string{"schema.sql"})
+	defer cleanupFunc()
+
+	tmpDir := t.TempDir()
+	err := pggen.Generate(
+		pggen.GenerateOptions{
+			ConnString: conn.Config().ConnString(),
+			QueryFiles: []string{"query.sql"},
+			OutputDir:  tmpDir,
+			GoPackage:  "numeric_external",
+			Language:   pggen.LangGo,
+			TypeOverrides: map[string]string{
+				"int4":    "int",
+				"int8":    "int",
+				"text":    "string",
+				"numeric": "github.com/shopspring/decimal.Decimal",
+			},
+		})
+	if err != nil {
+		t.Fatalf("Generate(): %s", err)
+	}
+
+	wantQueriesFile := "query.sql.go"
+	gotQueriesFile := filepath.Join(tmpDir, "query.sql.go")
+	assert.FileExists(t, gotQueriesFile,
+		"Generate() should emit query.sql.go")
+	wantQueries, err := ioutil.ReadFile(wantQueriesFile)
+	if err != nil {
+		t.Fatalf("read wanted query.go.sql: %s", err)
+	}
+	gotQueries, err := ioutil.ReadFile(gotQueriesFile)
+	if err != nil {
+		t.Fatalf("read generated query.go.sql: %s", err)
+	}
+	assert.Equalf(t, string(wantQueries), string(gotQueries),
+		"Got file %s; does not match contents of %s",
+		gotQueriesFile, wantQueriesFile)
+}

example/numeric_external/query.sql

@@ -0,0 +1,7 @@
+-- name: InsertNumeric :exec
+INSERT INTO numeric_external (num, num_arr)
+VALUES (pggen.arg('num'), pggen.arg('num_arr'));
+
+-- name: FindNumerics :many
+SELECT num, num_arr
+FROM numeric_external;