added single field "like" filtering using the ~ character along with …

…a unit test and an update to the README.md that details all supported filter operators (#13)

README.md

@@ -53,6 +53,15 @@ Any filter combination can be used here `filter.PAGINATION|filter.ORDER_BY` e.g.
 curl -X GET http://localhost:8080/users?page=1&limit=10&order_by=username&order_direction=asc&filter="name:John"
 ```
 
+## Supported filter operators
+- :   The equality operator `filter=username:John` matches only when the username is exactly `John`
+- \>  The greater than operator `filter=age>35` matches only when age is more than 35
+- \<  The less than operator `filter=salary<80000` matches only when salary is less than 80,000
+- \>= The greater than or equals to operator `filter=items>=100` matches only when items is at least 100
+- \<= The less than or equals to operator `filter=score<=100000` matches when score is 100,000 or lower
+- \!= The not equals to operator `state!=FAIL` matches when state has any value other than FAIL
+- \~  The like operator `filter=lastName~illi` matches when lastName contains the substring `illi`
+
 ## TODO list
 - [x] Write tests for the lib with CI integration
 - [x] Add support for case-insensitive search

gin-gorm-filter.go

@@ -104,7 +104,7 @@ func filterField(field reflect.StructField, phrase string) clause.Expression {
 	// re, err := regexp.Compile(fmt.Sprintf(`(?m)%v([:<>!=]{1,2})(\w{1,}).*`, paramName))
 	// for the current regex, the compound operators (such as >=) must come before the
 	// single operators (such as <) or they will be incorrectly identified
-	re, err := regexp.Compile(fmt.Sprintf(`(?m)%v(:|!=|>=|<=|>|<)([^,]*).*`, paramName))
+	re, err := regexp.Compile(fmt.Sprintf(`(?m)%v(:|!=|>=|<=|>|<|~)([^,]*).*`, paramName))
 	if err != nil {
 		return nil
 	}
@@ -121,6 +121,8 @@ func filterField(field reflect.StructField, phrase string) clause.Expression {
 			return clause.Gt{Column: columnName, Value: filterSubPhraseMatch[2]}
 		case "<":
 			return clause.Lt{Column: columnName, Value: filterSubPhraseMatch[2]}
+		case "~":
+			return clause.Like{Column: columnName, Value: filterSubPhraseMatch[2]}
 		default:
 			return clause.Eq{Column: columnName, Value: filterSubPhraseMatch[2]}
 		}

gin-gorm-filter_test.go

@@ -80,6 +80,23 @@ func (s *TestSuite) TestFiltersBasic() {
 	s.NoError(err)
 }
 
+// TestFiltersBasic is a test for basic filters functionality.
+func (s *TestSuite) TestFiltersLike() {
+	var users []User
+	ctx := gin.Context{}
+	ctx.Request = &http.Request{
+		URL: &url.URL{
+			RawQuery: "filter=login~samp",
+		},
+	}
+
+	s.mock.ExpectQuery(`^SELECT \* FROM "users" WHERE "Username" LIKE \$1 ORDER BY "id" DESC LIMIT \$2$`).
+		WithArgs("samp", 10).
+		WillReturnRows(sqlmock.NewRows([]string{"id", "Username", "FullName", "Email", "Password"}))
+	err := s.db.Model(&User{}).Scopes(FilterByQuery(&ctx, ALL)).Find(&users).Error
+	s.NoError(err)
+}
+
 // Filtering for a field that is not filtered should not be performed
 func (s *TestSuite) TestFiltersNotFilterable() {
 	var users []User