Merge pull request #45 from thedevsaddam/feature/offset-method

Add Offset method #42

jsonq.go

@@ -47,7 +47,8 @@ type JSONQ struct {
 	queryIndex       int                  // contains number of orWhere query call
 	queries          [][]query            // nested queries
 	attributes       []string             // select attributes that will be available in final resuls
-	limitRecords     int                  // number of records that willbe available in final result
+	offsetRecords    int                  // number of records that will be skipped in final result
+	limitRecords     int                  // number of records that will be available in final result
 	distinctProperty string               // contain the distinct attribute name
 	errors           []error              // contains all the errors when processing
 }
@@ -155,6 +156,28 @@ func (j *JSONQ) Select(properties ...string) *JSONQ {
 	return j
 }
 
+// Offset skips the number of records in result
+func (j *JSONQ) Offset(offset int) *JSONQ {
+	j.offsetRecords = offset
+	return j
+}
+
+// offset skips the records from result
+func (j *JSONQ) offset() *JSONQ {
+	if list, ok := j.jsonContent.([]interface{}); ok {
+		if j.offsetRecords <= 0 {
+			j.addError(fmt.Errorf("%d is invalid offset", j.offsetRecords))
+			return j
+		}
+		if len(list) > j.offsetRecords {
+			j.jsonContent = list[j.offsetRecords:]
+		} else {
+			j.jsonContent = make([]interface{}, 0)
+		}
+	}
+	return j
+}
+
 // Limit limits the number of records in result
 func (j *JSONQ) Limit(limit int) *JSONQ {
 	j.limitRecords = limit
@@ -508,6 +531,7 @@ func (j *JSONQ) reset() *JSONQ {
 	j.queries = make([][]query, 0)
 	j.attributes = make([]string, 0)
 	j.queryIndex = 0
+	j.offsetRecords = 0
 	j.limitRecords = 0
 	j.distinctProperty = ""
 	return j
@@ -524,6 +548,9 @@ func (j *JSONQ) Get() interface{} {
 	if j.distinctProperty != "" {
 		j.distinct()
 	}
+	if j.offsetRecords != 0 {
+		j.offset()
+	}
 	if j.limitRecords != 0 {
 		j.limit()
 	}

jsonq_test.go

@@ -241,6 +241,13 @@ func TestJSONQ_Select(t *testing.T) {
 	}
 }
 
+func TestJSONQ_Offset(t *testing.T) {
+	jq := New().Offset(3)
+	if jq.offsetRecords != 3 {
+		t.Error("failed to set offset records value")
+	}
+}
+
 func TestJSONQ_Limit(t *testing.T) {
 	jq := New().Limit(12)
 	if jq.limitRecords != 12 {
@@ -1219,6 +1226,33 @@ func TestJSONQ_Get_with_nested_invalid_property_in_Select_method_expecting_error
 	assertJSON(t, out, expected, "nested Select method using alias")
 }
 
+func TestJSONQ_Offset_method(t *testing.T) {
+	jq := New().JSONString(jsonStr).
+		From("vendor.items").
+		Offset(4)
+	out := jq.Get()
+	expected := `[{"id":5,"key":2300,"name":"HP core i5","price":850},{"id":6,"name":"HP core i7","price":950},{"id":null,"name":"HP core i3 SSD","price":850}]`
+	assertJSON(t, out, expected, "failed to offset records")
+}
+
+func TestJSONQ_Offset_Where_method(t *testing.T) {
+	jq := New().JSONString(jsonStr).
+		From("vendor.items").
+		Offset(4).WhereNotNil("id")
+	out := jq.Get()
+	expected := `[{"id":5,"key":2300,"name":"HP core i5","price":850},{"id":6,"name":"HP core i7","price":950}]`
+	assertJSON(t, out, expected, "failed to limit records")
+}
+
+func TestJSONQ_Offset_greater_than_the_original_value_with_Where_method(t *testing.T) {
+	jq := New().JSONString(jsonStr).
+		From("vendor.items").
+		Offset(40).WhereNotNil("id")
+	out := jq.Get()
+	expected := `[]`
+	assertJSON(t, out, expected, "failed to offset records when offset value is greater than the length of orignal result")
+}
+
 func TestJSONQ_Limit_method(t *testing.T) {
 	jq := New().JSONString(jsonStr).
 		From("vendor.items").
@@ -1237,6 +1271,15 @@ func TestJSONQ_Limit_Where_method(t *testing.T) {
 	assertJSON(t, out, expected, "failed to limit records")
 }
 
+func TestJSONQ_Offset_invalid_number_should_return_error(t *testing.T) {
+	jq := New().JSONString(jsonStr).
+		From("vendor.items").
+		Offset(-2)
+	jq.Get()
+	if jq.Error() == nil {
+		t.Error("failed to catch invalid offset error")
+	}
+}
 func TestJSONQ_Limit_invalid_number_should_return_error(t *testing.T) {
 	jq := New().JSONString(jsonStr).
 		From("vendor.items").