added db.TableForStruct

Author: ungerik

db/table.go

@@ -0,0 +1,30 @@
+package db
+
+import (
+	"fmt"
+	"reflect"
+)
+
+type Table struct{}
+
+var typeOfTable = reflect.TypeFor[Table]()
+
+func TableForStruct(t reflect.Type, tagKey string) (table string, err error) {
+	if t.Kind() != reflect.Struct {
+		return "", fmt.Errorf("db.StructTable: %s is not a struct", t)
+	}
+	if tagKey == "" {
+		return "", fmt.Errorf("db.StructTable: tagKey is empty")
+	}
+	for i := 0; i < t.NumField(); i++ {
+		field := t.Field(i)
+		if field.Anonymous && field.Type == typeOfTable {
+			table = field.Tag.Get(tagKey)
+			if table == "" {
+				return "", fmt.Errorf("db.StructTable: embedded db.Table has no tag '%s'", tagKey)
+			}
+			return table, nil
+		}
+	}
+	return "", fmt.Errorf("db.StructTable: struct type %s has no embedded db.Table field", t)
+}

db/table_test.go

@@ -0,0 +1,78 @@
+package db
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestTableForStruct(t *testing.T) {
+	tests := []struct {
+		name      string
+		t         reflect.Type
+		tagKey    string
+		wantTable string
+		wantErr   bool
+	}{
+		{
+			name: "OK",
+			t: reflect.TypeFor[struct {
+				Table `db:"table_name"`
+			}](),
+			tagKey:    "db",
+			wantTable: "table_name",
+		},
+		{
+			name: "more struct fields",
+			t: reflect.TypeFor[struct {
+				ID    int `db:"id"`
+				Table `db:"table_name"`
+				Value string `db:"value"`
+			}](),
+			tagKey:    "db",
+			wantTable: "table_name",
+		},
+		// Error cases
+		{
+			name:    "empty",
+			t:       reflect.TypeFor[struct{}](),
+			tagKey:  "db",
+			wantErr: true,
+		},
+		{
+			name: "no tagKey",
+			t: reflect.TypeFor[struct {
+				Table
+			}](),
+			tagKey:  "db",
+			wantErr: true,
+		},
+		{
+			name: "wrong tagKey",
+			t: reflect.TypeFor[struct {
+				Table `json:"table_name"`
+			}](),
+			tagKey:  "db",
+			wantErr: true,
+		},
+		{
+			name: "named field",
+			t: reflect.TypeFor[struct {
+				Table Table `db:"table_name"`
+			}](),
+			tagKey:  "db",
+			wantErr: true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotTable, err := TableForStruct(tt.t, tt.tagKey)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("TableForStruct(%s, %#v) error = %v, wantErr %v", tt.t, tt.tagKey, err, tt.wantErr)
+				return
+			}
+			if gotTable != tt.wantTable {
+				t.Errorf("TableForStruct(%s, %#v) = %v, want %v", tt.t, tt.tagKey, gotTable, tt.wantTable)
+			}
+		})
+	}
+}