Generate schema consts and scan func

Author: hlubek

README.md

@@ -41,6 +41,13 @@ go generate ./repository
 
 **Roll your own persistence code for full control and low abstraction**
 
+Structure your persistence code as it fits the project. A very simple and working approach is to have a bunch of
+functions that operator on the target type for finding, inserting, updating and deleting. Add more complex queries
+as you like in the same way. 
+
+There's no need to use Squirrel, but it helps to build correct SQL queries instead of relying on string manipulation
+and manually handling placeholders and arguments.
+
 *repository/customer_repository.go*
 ```go
 package repository
@@ -50,10 +57,12 @@ func FindCustomerByID(ctx context.Context, runner squirrel.BaseRunner, id uuid.U
 		Select(buildCustomerJson()).
 		From("customers").
 		LeftJoin("domains ON (domains.customer_id = customers.customer_id)").
-		Where(squirrel.Eq{"customers.customer_id": id}).
-		GroupBy("customers.customer_id").
+		// constants for read columns are generated by construct to prevent typos
+		Where(squirrel.Eq{customer_id: id}).
+		GroupBy(customer_id).
 		QueryRowContext(ctx)
-	return scanCustomerResult(row)
+	// customerScanJsonRow is generated by construct and will scan a JSON row result into the target type 
+	return customerScanJsonRow(row)
 }
 
 // CustomerChangeSet is generated by construct for handling partially filled models
@@ -69,7 +78,7 @@ func InsertCustomer(ctx context.Context, runner squirrel.BaseRunner, changeSet C
 func UpdateCustomer(ctx context.Context, runner squirrel.BaseRunner, id uuid.UUID, changeSet CustomerChangeSet) error {
 	res, err := queryBuilder(runner).
 		Update("customers").
-		Where(squirrel.Eq{"customer_id": id}).
+		Where(squirrel.Eq{customer_id: id}).
 		SetMap(changeSet.toMap()).
 		ExecContext(ctx)
 	if err != nil {
@@ -86,20 +95,13 @@ func buildCustomerJson() string {
 		Set("DomainCount", cjson.Exp("COUNT(domains.domain_id)")).
 		ToSql()
 }
+```
 
-func scanCustomerResult(row squirrel.RowScanner) (result domain.Customer, err error) {
-	var data []byte
-	if err := row.Scan(&data); err != nil {
-		if err == sql.ErrNoRows {
-			return result, ErrNotFound
-		}
-		return result, err
-	}
-
-	return result, json.Unmarshal(data, &result)
-}
+These are common functions that can be shared by all repository implementations:
 
-// These are common functions that can be shared by all repository implementations
+*repository/commong.go*
+```go
+package repository
 
 func queryBuilder(runner squirrel.BaseRunner) squirrel.StatementBuilderType {
 	return squirrel.StatementBuilder.

internal/fixtures/repository/mappings_mytype_gen.go

@@ -16,6 +16,8 @@ func Generate(m *StructMapping, goPackage string, goFile string, w io.Writer) (o
 
 	f.PackageComment("Code generated by construct, DO NOT EDIT.")
 
+	generateConstSchema(f, m)
+
 	generateSortFields(f, m)
 
 	// ChangeSet struct
@@ -99,7 +101,7 @@ func Generate(m *StructMapping, goPackage string, goFile string, w io.Writer) (o
 
 	generateDefaultSelectJsonObject(f, m)
 
-	// TODO Generate Schema for refactoring friendly access to fields
+	generateScanJsonRow(f, m)
 
 	ext := filepath.Ext(goFile)
 	baseFilename := goFile[0 : len(goFile)-len(ext)]
@@ -108,6 +110,20 @@ func Generate(m *StructMapping, goPackage string, goFile string, w io.Writer) (o
 	return outputFilename, f.Render(w)
 }
 
+func generateConstSchema(f *File, m *StructMapping) {
+	f.Const().DefsFunc(func(g *Group) {
+		for _, fm := range m.FieldMappings {
+			if fm.ReadColDef != nil {
+				g.Id(readColConstId(m, fm)).Op("=").Lit(fm.ReadColDef.Col)
+			}
+		}
+	})
+}
+
+func readColConstId(m *StructMapping, fm FieldMapping) string {
+	return firstToLower(m.MappingTypeName) + "_" + firstToLower(fm.Name)
+}
+
 func generateDefaultSelectJsonObject(f *File, m *StructMapping) {
 	varName := firstToLower(m.TargetName + "DefaultSelectJson")
 
@@ -126,6 +142,27 @@ func generateDefaultSelectJsonObject(f *File, m *StructMapping) {
 	}
 }
 
+func generateScanJsonRow(f *File, m *StructMapping) {
+	f.Func().Id(firstToLower(m.TargetName)+"ScanJsonRow").Params(
+		Id("row").Qual("github.com/networkteam/construct", "RowScanner"),
+	).Params(
+		Id("result").Qual(m.MappingTypePackage, m.MappingTypeName),
+		Id("err").Error(),
+	).Block(
+		Var().Id("data").Op("[]").Byte(),
+		If(
+			Id("err").Op(":=").Id("row").Dot("Scan").Call(Op("&").Id("data")),
+			Id("err").Op("!=").Nil(),
+		).Block(
+			If(Id("err").Op("==").Qual("database/sql", "ErrNoRows")).Block(
+				Return(Id("result"), Qual("github.com/networkteam/construct", "ErrNotFound")),
+			),
+			Return(Id("result"), Id("err")),
+		),
+		Return(Id("result"), Qual("encoding/json", "Unmarshal").Call(Id("data"), Op("&").Id("result"))),
+	)
+}
+
 func generateChangeSetStruct(f *File, m *StructMapping) (changeSetName string, err error) {
 	var structFields []Code
 
@@ -190,7 +227,7 @@ func generateSortFields(f *File, m *StructMapping) {
 	sortFieldDict := make(Dict)
 	for _, fm := range m.FieldMappings {
 		if fm.ReadColDef != nil && fm.ReadColDef.Sortable {
-			sortFieldDict[Lit(strings.ToLower(fm.Name))] = Lit(fm.ReadColDef.Col)
+			sortFieldDict[Lit(strings.ToLower(fm.Name))] = Id(readColConstId(m, fm))
 		}
 	}
 	f.Var().Id(firstToLower(m.TargetName + "SortFields")).Op("=").Map(String()).String().

internal/generate.go

@@ -0,0 +1,9 @@
+package construct
+
+import "errors"
+
+var ErrNotFound = errors.New("record not found")
+
+type RowScanner interface {
+	Scan(...interface{}) error
+}