Travailler avec la table d’attributs¶

Table view vs Form view¶

QGIS provides two view modes to easily manipulate data in the attribute table:

• the Table view, displaying values of multiple features in a tabular mode, each row representing a feature and each column a field;
• and the Form view which shows identifiers of features in a first panel and displays only the attributes of the clicked identifier in the second one. Form view uses the layer fields configuration (see Fields Properties).

You can switch from one mode to the other by clicking the convenient icon at the bottom right of the dialog.

You can also specify the Default view mode at the opening of the attribute table in Settings ‣ Options ‣ Data Sources menu. It can be ‘Remember last view’, ‘Table view’ or ‘Form view’.

Attribute table in form view (top) vs table view (bottom)

Configuring the columns¶

Right-click in a column header when in table view to have access to tools that help you configure what can be displayed in the attribute table and how.

Formatting of table cells using conditions¶

Conditional formatting settings can be used to highlight in the attribute table features you may want to put a particular focus on, using custom conditions on feature’s:

• geometry (e.g., identifying multi-parts features, small area ones or in a defined map extent...);
• or field value (e.g., comparing values to a threshold, identifying empty cells...)

You can enable the conditional formatting panel clicking on at the top right of the attributes window in table view (not available in form view).

The new panel allows user to add new rules to format rendering of Field or Full row. Adding new rule opens a form to define:

• the name of the rule;
• a condition using any of the expression builder functions;
• the formatting: it can be choosen from a list of predefined formats or created based on properties like:

  • couleurs d’arrière-plan et du texte;

  • utilisation d’une Icône;

  • texte en gras, italique, souligné ou barré;

  • police.

Mise en forme conditionnelle des cellules de la table d’attributs

Sélectionner des entités¶

In table view, each row in the attribute table displays the attributes of a unique feature in the layer. Selecting a row selects the feature and likewise, selecting a feature in the map canvas (in case of geometry enabled layer) selects the row in the attribute table. If the set of features selected in the map canvas (or attribute table) is changed, then the selection is also updated in the attribute table (or map canvas) accordingly.

Les lignes peuvent être sélectionnées en cliquant sur le numéro de ligne placé tout à gauche. Plusieurs lignes peuvent être sélectionnées en maintenant la touche Ctrl. Une sélection continue s’effectue en gardant appuyée la touche Shift et en cliquant sur une nouvelle ligne, toutes les lignes entre la première sélection et la dernière seront sélectionnées. Déplacer la position du curseur dans la table d’attributs en cliquant sur une cellule ne modifie pas la sélection des lignes. Modifier les entités sélectionnées depuis la carte ne modifie pas la position du curseur dans la table.

In form view of the attribute table, features are by default identified in the left panel by the value of their displayed field (see Propriétés des Infobulles). This identifier can be replaced using the drop-down list at the top of the panel, either by selecting an existing field or using a custom expression. You can also choose to sort the list of features from the drop-down menu.

Click a value in the left panel to display the feature’s attributes in the right one. To select a feature, you need to click inside the square symbol at the left of the identifier. By default, the symbol turns into yellow. Like in the table view, you can perform multiple feature selection using the keyboard combinations previously exposed.

Beyond selecting features with the mouse, you can perform automatic selection based on feature’s attribute using tools available in the attribute table toolbar, such as (see section Automatic selection and following one for more information and use case):

• Sélectionner à l’aide d’une expression...

• Sélectionner des entités par valeur...

• :guilabel:` Désélectionner toutes les entités`

• Sélectionner toutes les entités

• Inverser la sélection des entités.

It is also possible to select features using the Filtering and selecting features using forms.

Filtrer les entités¶

Once you have selected features in the attribute table, you may want to display only these records in the table. This can be easily done using the Show Selected Features item from the drop-down list at the bottom left of the attribute table dialog. This list offers the following filters:

• :guilabel:` Montrer toutes les entités`

• :guilabel:` Ne montrer que les entités sélectionnées`

• :guilabel:` Ne montrer que les entités visibles sur la carte`

• :guilabel:` Ne montrer que les entités nouvelles ou éditées`

• Field Filter - allows the user to filter based on value of a field: choose a column from a list, type a value and press Enter to filter. Then, only the matching features are shown in the attribute table.
• Advanced filter (Expression) - Opens the expression builder dialog. Within it, you can create complex expressions to match table rows. For example, you can filter the table using more that one field. See Expressions for more information.

It is also possible to filter features using the Filtering and selecting features using forms.

Filtering and selecting features using forms¶

Clicking the ^{Filter/Select features using form} or pressing Ctrl+F the attribute table dialog will switch to form view and all widgets are replaced with their search variant.

From this point onwards, this tool functionality is similar to the one described in the Sélectionner des Entités par Valeur, where you can find descriptions of all operators and selecting modes.

Moreover, in the attribute table case, there is also a Filter features button that allows filtering features instead of selecting them (by creating an Advanced Filter (Expression) for the user).

Attribute table filtered by the filter form

If there are already filtered features, you can refine the filter using the drop-down list next to the Filter features button. The options are:

• Filtre incluant (“AND”)

• Filtre exclusif (“OR”)

To clear the filter, either select Show all features option mentioned in Filtrer les entités, or click the clear the expression and click [Apply].

Saving selected features as new layer¶

The selected features can be saved as any OGR-supported vector format and also transformed into another coordinate reference system (CRS). In the contextual menu of the layer, from the Layers Panel, click on Save as to define the name of the output file, its format and CRS (see section Creating new layers from an existing layer). To save the selection ensure that the Save only selected features is selected. It is also possible to specify OGR creation options within the dialog.

Using the Field Calculator¶

The ^{Field Calculator} button in the attribute table allows you to perform calculations on the basis of existing attribute values or defined functions, for instance, to calculate length or area of geometry features. The results can be written to a new attribute field, a virtual field, or they can be used to update values in an existing field.

La calculatrice de champ fonctionne avec toutes les couches qui gèrent le mode édition. Lorsque vous cliquez sur le bouton de la calculatrice de champ, la fenêtre s’ouvre (voir figure_field_calculator). Si la couche n’est pas en mode édition, un avertissement s’affiche et l’utilisation de la calculatrice de champ basculera automatiquement la couche en édition avant d’effectuer le calcul.

Based on the Expression Builder dialog, the field calculator dialog offers a complete interface to define an expression and apply it to an existing or a newly created field. To use the field calculator dialog, you first must select whether you want to only update selected features, create a new attribute field where the results of the calculation will be added or update an existing field.

Calculatrice de champ

If you choose to add a new field, you need to enter a field name, a field type (integer, real, date or string) and if needed, the total field length and the field precision. For example, if you choose a field length of 10 and a field precision of 3, it means you have 6 digits before the dot, then the dot and another 3 digits for the precision.

L’exemple suivant montre comment la calculatrice de champs fonctionne. Il s’agit de calculer la longueur en km de la couche railroads issue de l’échantillon de données QGIS.

1. Chargez le fichier shapefile railroads.shp dans QGIS et ouvrez sa ^{Table d’Attributs}.

2. Cliquez sur ^{Basculer en mode édition} et ouvrez la ^{Calculatrice de champs}.

3. Cochez la case Créer un nouveau champ pour enregistrer le résultat des calculs dans un nouveau champ.

4. Ajoutez longueur dans le nom de ce champ, réel en tant que type et définissez une longueur de 10 et une précision de 3.

5. Double-cliquez maintenant sur la fonction $length de la catégorie Géometrie pour l’ajouter à la zone d’Expression.

6. Complete the expression by typing / 1000 in the Field calculator expression box and click [Ok].

7. Vous pouvez maintenant voir la nouvelle colonne longueur dans la table d’attributs.

Creating a Virtual Field¶

A virtual field is a field based on an expression calculated on the fly, meaning that its value is automatically updated as soon as the underlying parameter changes. The expression is set once; you no longer need to recalculate the field each time underlying values change. For example, you may want to use a virtual field if you need area to be evaluated as you digitize features or to automatically calculate a duration between dates that may change (e.g., using now() function).

Using the Quick Field Calculation Bar¶

While Field calculator is always available, the quick field calculation bar on top of the attribute table is only visible if the layer is in edit mode. Thanks to the expression engine, it offers a quicker access to edit an already existing field.

In quick field calculation bar, you simply need to:

• select the existing field name in the drop-down list
• fill the textbox with an expression you directly write or build using the expression button
• and click on [Update All], [Update Selected] or [Update Filtered] button according to your need.

Editing multiple fields¶

Contrairement aux outils précédents, le mode d’édition multiple permet d’éditer simultanément plusieurs champs de plusieurs entités. Une fois la couche basculée en mode édition, les options d’édition multiple sont accessibles:

• using the ^{Toggle multi edit mode} button from the toolbar inside the attribute table dialog,

• soit en sélectionnant depuis le menu Edition ‣ Modifier les attributs des entités sélectionnées.

Afin de modifier d’une traite plusieurs champs:

1. select the features you want to edit;

2. from the attribute table toolbar, click the button. This will toggle the dialog to its form view. Feature selection could also be made at this step;

3. at the right side of the attribute table, fields (and values) of selected features are shown. New widgets appear next to each field allowing for display of the current multi edit state:

   • the field contains different values for selected features. It’s shown empty and each feature will keep its original value. You can reset the value of the field from the drop-down list of the widget.
   • all selected features have the same value for this field and the value displayed in the form will be kept.
   • the field has been edited and the entered value will be applied to all the selected features. A message appears at the top of the dialog, inviting you to either apply or reset your modification.

   Clicking any of these widgets allows you to either set the current value for the field or reset to original value, meaning that you can roll back changes on a field-by-field basis.

4. make the changes to the fields you want and click on Apply changes in the upper message text or any other feature in the left panel.

Changes will apply to all selected features. If no feature is selected, the whole table is updated with your changes. Modifications are made as a single edit command. So pressing ^Undo will rollback the attribute changes for all selected features at once.

Mettre à jour des champs de plusieurs entités

Introducing 1-N relations¶

Comme exemple, nous prendrons une couche contenant toutes les régions de l’Alaska (des polygones) qui fournit quelques attributs sur le nom, le type de région et un identifiant unique (qui jouera le rôle de clé primaire).

Nous prenons ensuite une autre couche de point ou une table contenant des informations sur les aéroports localisés dans les régions. Si vous souhaitez accéder, depuis la couche des régions, vous devez créer une relation ‘un à plusieurs’, en utilisant des clés étrangères, car il y a plusieurs aéroports dans la plupart des régions.

Les régions d’Alaska contenant des aéroports

Defining 1-N relations (Relation Manager)¶

The first thing we are going to do is to let QGIS know about the relations between the layers. This is done in Project ‣ Project Properties.... Open the Relations tab and click on [Add Relation].

• name is going to be used as a title. It should be a human readable string, describing, what the relation is used for. We will just call say Airports in this case.
• referencing layer also considered as child layer, is the one with the foreign key field on it. In our case, this is the airports layer
• referencing field will say, which field points to the other layer so this is fk_region in this case
• referenced layer also considered as parent layer, is the one with the primary key, pointed to, so here it is the regions layer
• referenced field is the primary key of the referenced layer so it is ID
• id will be used for internal purposes and has to be unique. You may need it to build custom forms. If you leave it empty, one will be generated for you but you can assign one yourself to get one that is easier to handle.

Gestionnaire de Relations

Forms for 1-N relations¶

Maintenant que QGIS a bien généré la relation, le formulaire d’édition va être amélioré. Nous n’avons pas modifié le formulaire d’édition par défaut (généré automatiquement), une nouvelle zone va simplement être ajoutée au formulaire. Sélectionnez la couche de régions dans la légende et utilisez l’outil d’identification. Selon vos préférences, le formulaire s’ouvre directement ou vous devez le faire via la zone d’identification qui s’affiche.

Formulaire de la couche des régions affichant la relation avec les aéroports

As you can see, the airports assigned to this particular region are all shown in a table. And there are also some buttons available. Let’s review them shortly

• Le bouton permet de passer en mode édition. Soyez conscients qu’il active le mode édition de la couche des aéroports bien qu’il soit situé dans le formulaire de la couche des régions. La table affiche bien les entités de la couche des aéroports.

• The button will add a new feature to the airport layer. And it will assign the new airport to the current region by default.
• The button will delete the selected airport permanently.

• Le bouton ouvre une nouvelle fenêtre où vous pouvez sélectionner des aéroports existants et qui seront ensuite attribués à la région identifiée. Ceci est pratique lorsque vous assignez par erreur la mauvaise région à un aéroport.

• Le bouton permet de supprimer le lien entre l’aéroport sélectionné et la région identifiée, le laissant non assigné (la clé étrangère devient alors NULL).

• The two buttons to the right switch between table view and form view where the later let’s you view all the airports in their respective form.

If you work on the airport table, a new widget type is available which lets you embed the feature form of the referenced region on the feature form of the airports. It can be used when you open the layer properties of the airports table, switch to the Fields menu and change the widget type of the foreign key field ‘fk_region’ to Relation Reference.

Vous devriez ainsi voir que le formulaire de la région est inclus dans celui d’un aéroport et il vous permet de modifier la région assignée à l’aéroport.

Formulaire d’identification d’un aéroport et de sa région associée

Introducing many-to-many (N-M) relations¶

N-M relations are many-to-many relation between two tables. For instance, the airports and airlines layers: an airport receives several airline companies and an airline company flies to several airports.

In such case, we need a pivot table to list all airlines for all airports. In QGIS, you should setup two one-to-many relations as explained above:

• a relation between airlines table and the pivot table;
• and a second one between airports table and the pivot table.

When we add a new child (i.e. a company to an airport), QGIS will add a new row in the pivot table and in the airlines table. If we link a company to an airport, QGIS will only add a row in the pivot table.

In case you want to remove a link, an airline or an airport, QGIS won’t remove the row in the pivot table. The database administrator should add a ON DELETE CASCADE instruction in the foreign key constraint:

ALTER TABLE location.airlines
ADD CONSTRAINT location_airlines_airports_id_fkey
   FOREIGN KEY (id)
      REFERENCES location.airports(id)
         ON DELETE CASCADE;

Finally, adding such relations in a form is done in the same way that for a one-to-many relation. The Relations panel in the Fields properties of the vector layer will let the user add the relation in the form. It will appear as a Many to many relation.