fix🐛: refuse to generate a table whose key is not one column

The templates address a row by a single key: one field on the model, one
path parameter, one value per row in a delete. A table with no primary key
rendered a model whose GetId returned an empty field name, and a composite
key was silently narrowed to whichever of its columns the importer read
last. Both wrote files that break the build of the whole module.

Preview and NOActionsGen now check first and return an error naming the
table and, for a composite key, its columns. Nothing is written.

app/other/apis/tools/gen.go

@@ -131,6 +131,10 @@ func (e Gen) Preview(c *gin.Context) {
 	// are not interchangeable stand-ins for each other and should not be
 	// assumed to be.
 	tab.MLTBName = strings.Replace(tab.TBName, "_", "-", -1)
+	if err := requireSinglePrimaryKey(tab); err != nil {
+		e.Error(500, err, err.Error())
+		return
+	}
 	// R2: infer a width for any column the config page left at colWidth's 0
 	// sentinel, before vue.go.template reads .ColWidth - see column_width.go.
 	applyInferredColumnWidths(tab.Columns)
@@ -221,6 +225,10 @@ func (e Gen) NOActionsGen(c *gin.Context, tab tools.SysTables) {
 	e.Context = c
 	log := e.GetLogger()
 	tab.MLTBName = strings.Replace(tab.TBName, "_", "-", -1)
+	if err := requireSinglePrimaryKey(tab); err != nil {
+		e.Error(500, err, err.Error())
+		return
+	}
 	// R2: see the matching call and comment in Preview above.
 	applyInferredColumnWidths(tab.Columns)
 
@@ -502,3 +510,26 @@ func (e Gen) GenMenuAndApi(c *gin.Context) {
 
 	e.OK("", "数据生成成功！")
 }
+
+// requireSinglePrimaryKey refuses a table whose primary key is not exactly one
+// column. The templates address a row by a single key - one field on the
+// model, one path parameter, one value per row in a delete - so a table with
+// no primary key, or a composite one, has no shape they can render: generating
+// it anyway writes a model whose GetId names nothing, or silently keys the
+// whole table on whichever key column happened to be imported last.
+func requireSinglePrimaryKey(tab tools.SysTables) error {
+	var keys []string
+	for _, c := range tab.Columns {
+		if c.Pk {
+			keys = append(keys, c.ColumnName)
+		}
+	}
+	switch len(keys) {
+	case 1:
+		return nil
+	case 0:
+		return fmt.Errorf("表 %s 没有主键，代码生成需要恰好一个主键列", tab.TBName)
+	default:
+		return fmt.Errorf("表 %s 是联合主键（%s），代码生成需要恰好一个主键列", tab.TBName, strings.Join(keys, ", "))
+	}
+}