Add support for arrays in the spatialite provider

New versions of GDAL/OGR (since trunk@35289) convert list types (StringList,
IntegerList, Integer64List and RealList) to a JSON string when it stores a
Spatialite table. It sets the column type as JSONSTRINGLIST, JSONINTEGERLIST,
JSONINTEGER64LIST or JSONREALLIST.

Author: Patrick Valsecchi

python/core/qgsjsonutils.sip

@@ -197,4 +197,11 @@ class QgsJSONUtils
      * @param feature feature to export
      */
     static QString exportAttributes( const QgsFeature& feature );
+
+    /** Parse a simple array (depth=1).
+     * @param json the JSON to parse
+     * @param type the type of the elements
+     * @note added in QGIS 3.0
+     */
+    static QVariantList parseArray( const QString& json, QVariant::Type type );
 };

src/core/qgsjsonutils.cpp

@@ -309,3 +309,82 @@ QString QgsJSONUtils::exportAttributes( const QgsFeature& feature )
   return attrs.prepend( '{' ).append( '}' );
 }
 
+
+namespace  //TODO: remove when we switch off Qt4
+{
+  void jumpSpace( const QString& txt, int& i )
+  {
+    while ( i < txt.length() && txt.at( i ).isSpace() ) ++i;
+  }
+
+  static QString getNextString( const QString& txt, int& i )
+  {
+    jumpSpace( txt, i );
+    QString cur = txt.mid( i );
+    if ( cur.startsWith( '"' ) )
+    { //quoted element
+      QRegExp stringRe( "^\"((?:\\\\.|[^\"\\\\])*)\".*" );
+      if ( !stringRe.exactMatch( cur ) )
+      {
+        return QString::null;
+      }
+      i += stringRe.cap( 1 ).length() + 2;
+      jumpSpace( txt, i );
+      if ( !txt.mid( i ).startsWith( ',' ) && !txt.mid( i ).startsWith( ']' ) && i < txt.length() )
+      {
+        return QString::null;
+      }
+      i += 1;  // jump the separator
+
+      return stringRe.cap( 1 )
+             .replace( "\\\"", "\"" )
+             .replace( "\\r", "\r" )
+             .replace( "\\b", "\b" )
+             .replace( "\\t", "\t" )
+             .replace( "\\/", "/" )
+             .replace( "\\n", "\n" )
+             .replace( "\\\\", "\\" );
+    }
+    else
+    { //unquoted element
+      QString ret;
+      int sepPos = cur.indexOf( ',' );
+      if ( sepPos < 0 ) sepPos = cur.indexOf( ']' );
+      if ( sepPos < 0 )
+      {
+        i += cur.length();
+        return cur.trimmed();
+      }
+      i += sepPos + 1;
+      return cur.left( sepPos ).trimmed();
+    }
+  }
+}
+
+QVariantList QgsJSONUtils::parseArray( const QString& json, QVariant::Type type )
+{
+  // TODO: switch to the Qt parser when we switch off Qt4
+  QVariantList result;
+  int i = 0;
+  jumpSpace( json, i );
+  if ( json.at( i++ ) != '[' )
+  {
+    return result;
+  }
+  while ( i < json.length() )
+  {
+    jumpSpace( json, i );
+    if ( json.at( i ) == ']' )
+    {
+      return result;
+    }
+    const QString value = getNextString( json, i );
+    if ( value.isNull() )
+    {
+      break;
+    }
+    QVariant variant( value );
+    if ( variant.convert( type ) ) result.append( variant );
+  }
+  return result;
+}

src/core/qgsjsonutils.h

@@ -240,6 +240,12 @@ class CORE_EXPORT QgsJSONUtils
      */
     static QString exportAttributes( const QgsFeature& feature );
 
+    /** Parse a simple array (depth=1).
+     * @param json the JSON to parse
+     * @param type the type of the elements
+     * @note added in QGIS 3.0
+     */
+    static QVariantList parseArray( const QString& json, QVariant::Type type );
 };
 
 #endif // QGSJSONUTILS_H

src/providers/spatialite/qgsspatialitefeatureiterator.cpp

@@ -19,9 +19,11 @@
 #include "qgsspatialiteprovider.h"
 #include "qgssqliteexpressioncompiler.h"
 
-#include "qgsgeometry.h"
-#include "qgslogger.h"
-#include "qgsmessagelog.h"
+#include <qgsgeometry.h>
+#include <qgslogger.h>
+#include <qgsmessagelog.h>
+#include <qgsjsonutils.h>
+
 #include <QSettings>
 
 QgsSpatiaLiteFeatureIterator::QgsSpatiaLiteFeatureIterator( QgsSpatiaLiteFeatureSource* source, bool ownSource, const QgsFeatureRequest& request )
@@ -499,22 +501,24 @@ bool QgsSpatiaLiteFeatureIterator::getFeature( sqlite3_stmt *stmt, QgsFeature &f
       {
         if ( ic <= mRequest.subsetOfAttributes().size() )
         {
-          int attrIndex = mRequest.subsetOfAttributes()[ic-1];
-          feature.setAttribute( attrIndex, getFeatureAttribute( stmt, ic, mSource->mFields.at( attrIndex ).type() ) );
+          const int attrIndex = mRequest.subsetOfAttributes()[ic-1];
+          const QgsField field = mSource->mFields.at( attrIndex );
+          feature.setAttribute( attrIndex, getFeatureAttribute( stmt, ic, field.type(), field.subType() ) );
         }
       }
       else
       {
-        int attrIndex = ic - 1;
-        feature.setAttribute( attrIndex, getFeatureAttribute( stmt, ic, mSource->mFields.at( attrIndex ).type() ) );
+        const int attrIndex = ic - 1;
+        const QgsField field = mSource->mFields.at( attrIndex );
+        feature.setAttribute( attrIndex, getFeatureAttribute( stmt, ic, field.type(), field.subType() ) );
       }
     }
   }
 
   return true;
 }
 
-QVariant QgsSpatiaLiteFeatureIterator::getFeatureAttribute( sqlite3_stmt* stmt, int ic, QVariant::Type type )
+QVariant QgsSpatiaLiteFeatureIterator::getFeatureAttribute( sqlite3_stmt* stmt, int ic, QVariant::Type type, QVariant::Type subType )
 {
   if ( sqlite3_column_type( stmt, ic ) == SQLITE_INTEGER )
   {
@@ -539,8 +543,14 @@ QVariant QgsSpatiaLiteFeatureIterator::getFeatureAttribute( sqlite3_stmt* stmt,
   if ( sqlite3_column_type( stmt, ic ) == SQLITE_TEXT )
   {
     // TEXT value
-    const char *txt = ( const char * ) sqlite3_column_text( stmt, ic );
-    return QString::fromUtf8( txt );
+    const QString txt = QString::fromUtf8(( const char * ) sqlite3_column_text( stmt, ic ) );
+    if ( type == QVariant::List || type == QVariant::StringList )
+    { // assume arrays are stored as JSON
+      QVariant result = QVariant( QgsJSONUtils::parseArray( txt, subType ) );
+      result.convert( type );
+      return result;
+    }
+    return txt;
   }
 
   // assuming NULL

src/providers/spatialite/qgsspatialitefeatureiterator.h

@@ -83,7 +83,7 @@ class QgsSpatiaLiteFeatureIterator : public QgsAbstractFeatureIteratorFromSource
     QString quotedPrimaryKey();
     bool getFeature( sqlite3_stmt *stmt, QgsFeature &feature );
     QString fieldName( const QgsField& fld );
-    QVariant getFeatureAttribute( sqlite3_stmt* stmt, int ic, QVariant::Type type );
+    QVariant getFeatureAttribute( sqlite3_stmt* stmt, int ic, QVariant::Type type, QVariant::Type subType );
     void getFeatureGeometry( sqlite3_stmt* stmt, int ic, QgsFeature& feature );
 
     //! wrapper of the SQLite database connection