Support :many key=group_id to return a map instead of a slice

issue #2353

internal/codegen/golang/query.go

@@ -200,6 +200,8 @@ type Query struct {
 	SourceName   string
 	Ret          QueryValue
 	Arg          QueryValue
+	ManyKey      string // Taken from CmdParams.ManyKey, the map-key for :many. If empty a slice should be returned.
+	ManyKeyType  string // The Go type of ManyKey
 	// Used for :copyfrom
 	Table *plugin.Identifier
 }
@@ -219,3 +221,23 @@ func (q Query) TableIdentifier() string {
 	}
 	return "[]string{" + strings.Join(escapedNames, ", ") + "}"
 }
+
+func (v Query) DefineRetTypeMultiple() string {
+	if v.ManyKey != "" {
+		return "map[" + v.ManyKeyType + "]" + v.Ret.DefineType()
+	}
+	return "[]" + v.Ret.DefineType()
+}
+
+func (v Query) HasManyKey() bool {
+	return v.ManyKey != ""
+}
+
+func (v Query) ManyKeyField() string {
+	for _, f := range v.Ret.Struct.Fields {
+		if f.DBName == v.ManyKey {
+			return v.Ret.Name + "." + f.Name
+		}
+	}
+	panic("couldn't find :many-key in struct fields")
+}

internal/codegen/golang/result.go

@@ -247,6 +247,9 @@ func buildQueries(req *plugin.CodeGenRequest, structs []Struct) ([]Query, error)
 		}
 
 		if len(query.Columns) == 1 && query.Columns[0].EmbedTable == nil {
+			if query.CmdParams.GetManyKey() != "" {
+				return nil, fmt.Errorf(":many key=%s query %s has only one column", query.CmdParams.GetManyKey(), query.Name)
+			}
 			c := query.Columns[0]
 			name := columnName(c, 0)
 			if c.IsFuncCall {
@@ -305,6 +308,18 @@ func buildQueries(req *plugin.CodeGenRequest, structs []Struct) ([]Query, error)
 				SQLDriver:   sqlpkg,
 				EmitPointer: req.Settings.Go.EmitResultStructPointers,
 			}
+			if query.CmdParams.GetManyKey() != "" {
+				gq.ManyKey = query.CmdParams.GetManyKey()
+				for _, c := range gs.Fields {
+					if c.DBName == gq.ManyKey {
+						gq.ManyKeyType = c.Type
+						break
+					}
+				}
+				if gq.ManyKeyType == "" {
+					return nil, fmt.Errorf("can not find key column %q in query %s", gq.ManyKey, gq.MethodName)
+				}
+			}
 		}
 
 		qs = append(qs, gq)

internal/codegen/golang/templates/stdlib/queryCode.tmpl

@@ -35,23 +35,27 @@ func (q *Queries) {{.MethodName}}(ctx context.Context, {{ dbarg }} {{.Arg.Pair}}
 {{if eq .Cmd ":many"}}
 {{range .Comments}}//{{.}}
 {{end -}}
-func (q *Queries) {{.MethodName}}(ctx context.Context, {{ dbarg }} {{.Arg.Pair}}) ([]{{.Ret.DefineType}}, error) {
+func (q *Queries) {{.MethodName}}(ctx context.Context, {{ dbarg }} {{.Arg.Pair}}) ({{.DefineRetTypeMultiple}}, error) {
     {{- template "queryCodeStdExec" . }}
     if err != nil {
         return nil, err
     }
     defer rows.Close()
-    {{- if $.EmitEmptySlices}}
-    items := []{{.Ret.DefineType}}{}
+    {{- if (or $.EmitEmptySlices .HasManyKey)}}
+    items := {{.DefineRetTypeMultiple}}{}
     {{else}}
-    var items []{{.Ret.DefineType}}
+    var items {{.DefineRetTypeMultiple}}
     {{end -}}
     for rows.Next() {
         var {{.Ret.Name}} {{.Ret.Type}}
         if err := rows.Scan({{.Ret.Scan}}); err != nil {
             return nil, err
         }
+        {{- if .HasManyKey}}
+        items[{{.ManyKeyField}}] = {{.Ret.ReturnName}}
+        {{else}}
         items = append(items, {{.Ret.ReturnName}})
+        {{end -}}
     }
     if err := rows.Close(); err != nil {
         return nil, err

internal/endtoend/testdata/manykey/stdlib/query.sql

@@ -0,0 +1,7 @@
+CREATE TABLE foo (
+	group_id INT NOT NULL,
+	score INT NOT NULL
+);
+
+-- name: SelectScoreSums :many key=group_id
+SELECT group_id, SUM(score) FROM foo GROUP BY group_id;

internal/endtoend/testdata/manykey/stdlib/sqlc.json

@@ -0,0 +1,11 @@
+{
+  "version": "1",
+  "packages": [
+    {
+      "path": "go",
+      "name": "querytest",
+      "schema": "query.sql",
+      "queries": "query.sql"
+    }
+  ]
+}