Allow query string handling which contains only not must

fixes #193

error.go

@@ -16,7 +16,7 @@ const (
 	ErrorIndexMetaMissing
 	ErrorIndexMetaCorrupt
 	ErrorDisjunctionFewerThanMinClauses
-	ErrorBooleanQueryNeedsMustOrShould
+	ErrorBooleanQueryNeedsMustOrShouldOrNotMust
 	ErrorNumericQueryNoBounds
 	ErrorPhraseQueryNoTerms
 	ErrorUnknownQueryType
@@ -35,17 +35,17 @@ func (e Error) Error() string {
 }
 
 var errorMessages = map[int]string{
-	int(ErrorIndexPathExists):                "cannot create new index, path already exists",
-	int(ErrorIndexPathDoesNotExist):          "cannot open index, path does not exist",
-	int(ErrorIndexMetaMissing):               "cannot open index, metadata missing",
-	int(ErrorIndexMetaCorrupt):               "cannot open index, metadata corrupt",
-	int(ErrorDisjunctionFewerThanMinClauses): "disjunction query has fewer than the minimum number of clauses to satisfy",
-	int(ErrorBooleanQueryNeedsMustOrShould):  "boolean query must contain at least one must or should clause",
-	int(ErrorNumericQueryNoBounds):           "numeric range query must specify min or max",
-	int(ErrorPhraseQueryNoTerms):             "phrase query must contain at least one term",
-	int(ErrorUnknownQueryType):               "unknown query type",
-	int(ErrorUnknownStorageType):             "unknown storage type",
-	int(ErrorIndexClosed):                    "index is closed",
-	int(ErrorAliasMulti):                     "cannot perform single index operation on multiple index alias",
-	int(ErrorAliasEmpty):                     "cannot perform operation on empty alias",
+	int(ErrorIndexPathExists):                        "cannot create new index, path already exists",
+	int(ErrorIndexPathDoesNotExist):                  "cannot open index, path does not exist",
+	int(ErrorIndexMetaMissing):                       "cannot open index, metadata missing",
+	int(ErrorIndexMetaCorrupt):                       "cannot open index, metadata corrupt",
+	int(ErrorDisjunctionFewerThanMinClauses):         "disjunction query has fewer than the minimum number of clauses to satisfy",
+	int(ErrorBooleanQueryNeedsMustOrShouldOrNotMust): "boolean query must contain at least one must or should or not must clause",
+	int(ErrorNumericQueryNoBounds):                   "numeric range query must specify min or max",
+	int(ErrorPhraseQueryNoTerms):                     "phrase query must contain at least one term",
+	int(ErrorUnknownQueryType):                       "unknown query type",
+	int(ErrorUnknownStorageType):                     "unknown storage type",
+	int(ErrorIndexClosed):                            "index is closed",
+	int(ErrorAliasMulti):                             "cannot perform single index operation on multiple index alias",
+	int(ErrorAliasEmpty):                             "cannot perform operation on empty alias",
 }

query_boolean.go

@@ -96,6 +96,16 @@ func (q *booleanQuery) SetBoost(b float64) Query {
 
 func (q *booleanQuery) Searcher(i index.IndexReader, m *IndexMapping, explain bool) (search.Searcher, error) {
 	var err error
+	var mustNotSearcher search.Searcher
+	if q.MustNot != nil {
+		mustNotSearcher, err = q.MustNot.Searcher(i, m, explain)
+		if err != nil {
+			return nil, err
+		}
+		if q.Must == nil && q.Should == nil {
+			q.Must = NewMatchAllQuery()
+		}
+	}
 
 	var mustSearcher search.Searcher
 	if q.Must != nil {
@@ -112,15 +122,6 @@ func (q *booleanQuery) Searcher(i index.IndexReader, m *IndexMapping, explain bo
 			return nil, err
 		}
 	}
-
-	var mustNotSearcher search.Searcher
-	if q.MustNot != nil {
-		mustNotSearcher, err = q.MustNot.Searcher(i, m, explain)
-		if err != nil {
-			return nil, err
-		}
-	}
-
 	return searchers.NewBooleanSearcher(i, mustSearcher, shouldSearcher, mustNotSearcher, explain)
 }
 
@@ -143,8 +144,8 @@ func (q *booleanQuery) Validate() error {
 			return err
 		}
 	}
-	if q.Must == nil && q.Should == nil {
-		return ErrorBooleanQueryNeedsMustOrShould
+	if q.Must == nil && q.Should == nil && q.MustNot == nil {
+		return ErrorBooleanQueryNeedsMustOrShouldOrNotMust
 	}
 	return nil
 }

query_test.go

@@ -192,14 +192,28 @@ func TestQueryValidate(t *testing.T) {
 				nil,
 				nil,
 				[]Query{NewMatchQuery("devon").SetField("desc")}),
-			err: ErrorBooleanQueryNeedsMustOrShould,
+			err: nil,
 		},
 		{
 			query: NewBooleanQuery(
 				[]Query{},
 				[]Query{},
 				[]Query{NewMatchQuery("devon").SetField("desc")}),
-			err: ErrorBooleanQueryNeedsMustOrShould,
+			err: nil,
+		},
+		{
+			query: NewBooleanQuery(
+				nil,
+				nil,
+				nil),
+			err: ErrorBooleanQueryNeedsMustOrShouldOrNotMust,
+		},
+		{
+			query: NewBooleanQuery(
+				[]Query{},
+				[]Query{},
+				[]Query{}),
+			err: ErrorBooleanQueryNeedsMustOrShouldOrNotMust,
 		},
 		{
 			query: NewBooleanQueryMinShould(