Add qb.ContainsKey to query keys in a map (#57)

qb: add ContainsKey and ContainsKeyNamed

qb/cmp.go

@@ -19,6 +19,7 @@ const (
 	geq
 	in
 	cnt
+	cntKey
 )
 
 // Cmp if a filtering comparator that is used in WHERE and IF clauses.
@@ -47,6 +48,8 @@ func (c Cmp) writeCql(cql *bytes.Buffer) (names []string) {
 		cql.WriteString(" IN ")
 	case cnt:
 		cql.WriteString(" CONTAINS ")
+	case cntKey:
+		cql.WriteString(" CONTAINS KEY ")
 	}
 	return c.value.writeCql(cql)
 }
@@ -267,6 +270,15 @@ func Contains(column string) Cmp {
 	}
 }
 
+// ContainsKey produces column CONTAINS KEY ?.
+func ContainsKey(column string) Cmp {
+	return Cmp{
+		op:     cntKey,
+		column: column,
+		value:  param(column),
+	}
+}
+
 // ContainsNamed produces column CONTAINS ? with a custom parameter name.
 func ContainsNamed(column, name string) Cmp {
 	return Cmp{
@@ -276,6 +288,15 @@ func ContainsNamed(column, name string) Cmp {
 	}
 }
 
+// ContainsKeyNamed produces column CONTAINS KEY ? with a custom parameter name.
+func ContainsKeyNamed(column, name string) Cmp {
+	return Cmp{
+		op:     cntKey,
+		column: column,
+		value:  param(name),
+	}
+}
+
 // ContainsLit produces column CONTAINS literal and does not add a parameter to the query.
 func ContainsLit(column, literal string) Cmp {
 	return Cmp{

qb/cmp_test.go

@@ -53,6 +53,11 @@ func TestCmp(t *testing.T) {
 			S: "cnt CONTAINS ?",
 			N: []string{"cnt"},
 		},
+		{
+			C: ContainsKey("cntKey"),
+			S: "cntKey CONTAINS KEY ?",
+			N: []string{"cntKey"},
+		},
 
 		// Custom bind names
 		{
@@ -90,6 +95,11 @@ func TestCmp(t *testing.T) {
 			S: "cnt CONTAINS ?",
 			N: []string{"name"},
 		},
+		{
+			C: ContainsKeyNamed("cntKey", "name"),
+			S: "cntKey CONTAINS KEY ?",
+			N: []string{"name"},
+		},
 
 		// Literals
 		{