lib/sql: add method WhereHolder to Meta type

The WhereHolder method generate string of holder, for example "$1,$2,...",
based on number of item added with [Meta.AddWhere].
Similar to method Holders but for where condition.

2 files changed, 38 insertions, 0 deletions

diff --git a/lib/sql/meta.go b/lib/sql/meta.go
index 7ce51f67..db0e2aed 100644
--- a/lib/sql/meta.go
+++ b/lib/sql/meta.go
@@ -25,6 +25,10 @@ type Meta struct {
 	// select.
 	ListValue []any
 
+	// ListWhereHolder contains list of column holder, as in "?" or
+	// "$x", depends on driver; expanded by calling AddWhere.
+	ListWhereHolder []string
+
 	// ListWhereValue contains list of values for where condition.
 	ListWhereValue []any
 }
@@ -55,6 +59,13 @@ func (meta *Meta) Add(colName string, val any) {
 // It return the length of ListWhereValue in list after addition.
 func (meta *Meta) AddWhere(val any) int {
 	meta.ListWhereValue = append(meta.ListWhereValue, val)
+
+	if meta.driver == DriverNamePostgres {
+		meta.ListWhereHolder = append(meta.ListWhereHolder, fmt.Sprintf(`$%d`, len(meta.ListWhereValue)))
+	} else {
+		meta.ListWhereHolder = append(meta.ListWhereHolder, DefaultPlaceHolder)
+	}
+
 	return len(meta.ListWhereValue)
 }
 
@@ -82,3 +93,10 @@ func (meta *Meta) UpdateFields() string {
 	}
 	return sb.String()
 }
+
+// WhereHolders generate string of holder, for example "$1,$2, ...", based
+// on number of item added with [Meta.AddWhere].
+// Similar to method Holders but for where condition.
+func (meta *Meta) WhereHolders() string {
+	return strings.Join(meta.ListWhereHolder, `,`)
+}
diff --git a/lib/sql/meta_example_test.go b/lib/sql/meta_example_test.go
index 8f85b671..499a79fd 100644
--- a/lib/sql/meta_example_test.go
+++ b/lib/sql/meta_example_test.go
@@ -71,7 +71,27 @@ func ExampleMeta_AddWhere() {
 
 	idx = meta.AddWhere(vals[1])
 	fmt.Println(idx, meta.ListWhereValue)
+
 	// Output:
 	// 1 [1000]
 	// 2 [1000 name]
 }
+
+func ExampleMeta_WhereHolders() {
+	var (
+		meta = sql.NewMeta(sql.DriverNamePostgres)
+		vals = []any{
+			int(1000),
+			string(`name`),
+		}
+		v any
+	)
+
+	for _, v = range vals {
+		meta.AddWhere(v)
+	}
+	fmt.Println(meta.WhereHolders())
+
+	// Output:
+	// $1,$2
+}