# Advanced Form Configuration
TIP
You can follow the examples in this section by cloning the following projects:
In addition to the edit widgets, extra configuration can be done to the fields and form layout to make the data collection easier and more consistent. For example: setting a default value, conditional visibility and constraint enforcement.
# Form layout
If your form contains more than a handful number of fields, it becomes difficult to navigate and enter or view the data. In this section, we can change the layout in QGIS.
# QGIS
To set form layout, we are going to use Drag-n-Drop designer:
- Download and open
documentation/form_setup (opens new window) in QGIS - From the layer panel, right-click on survey layer and select Properties
- In the new window, select Attributes form
- From the top of the drop-down menu, select Drag-n-Drop Designer
We can add multiple groups and move Fields from the left column to the newly generated groups.
In this example, we have created the following two groups and a subgroup:
- Information
- Location
- Data
The form will appear as below in QGIS now:
We can set the visibility of Location tab depending on the value of survey field:
- If survey is set to False, Location tab will not be present
- If survey is set to True, Location tab will appear
To set the visibility of Location depending on the value of survey:
- Select Location from the Form Layout column
- Select the option for Control Visibility by Expression
- Type the following expression in the box below:
"survey" IS TRUE
# Mergin Maps Input
To view the new layout in Input:
Open Input on your device and from Projects > Explore download documentation\form_setup
Open the project
Select Record and add a point
The form will appear and you can see 3 tabs in your forms
# Default value
To have prepopulated values within the field (e.g. name of the surveyor, date/time of the survey, latitude and longitude of the feature):
The default value can be a text, number or a QGIS expression. In the example below, we are going to set the default values for x and y field to be longitude and latitude.
# QGIS
To set up the default value for x field:
- Download and open documentation/form_setup (opens new window) in QGIS
- From the layer panel, right-click on survey layer and select Properties
- In the new window, select Attributes form
- Select x field under the right column (Available Widgets)
- Under the Widget Display:
- Set the Alias to Longitude
- Under Defaults:
- For Default value type: x( transform( $geometry, 'EPSG:3857', 'EPSG:4326'))
- Select the option to Apply default value on update
Note that the expression transforms the point from EPSG:3857 (map and layer coordinate reference system) to EPSG:4326.
Repeat the same for y field and set the default value to y( transform( $geometry, 'EPSG:3857', 'EPSG:4326'))
Ensure to save and synchronise your project.
# Mergin Maps Input
To see the default values in Input:
- Open Input on your device and from Projects > Explore download documentation/form_setup
- Open the project
- Select Record and add a point
- The form will appear
- Under Location tab, you can see the default prepopulated values :
# Constraints
When collecting data, you may want to apply constraints to certain field(s) so that the correct information is entered.
# QGIS
To set up the default value for x field:
- Download and open documentation/form_setup (opens new window) in QGIS
- From the layer panel, right-click on survey layer and select Properties
- In the new window, select Attributes form
- Select number field under the right column (Available Widgets)
- Under the Constraints:
- Select Not null
- Select Enforce not null constraints
- For Expression type "number" >= 1
- Select Enforce expression constraint
# Mergin Maps Input
- Open Input on your device and from Projects > Explore download documentation/form_setup
- Open the project
- Select Record and add a point
- The form will appear
- Under Data tab, you need to set the Number of plants: and the value should be more than or equal 1.
# Advanced value relation with drill-down forms
Cascade or drill-down forms are the types of forms that the values listed in one field depend on the value selected in another field.
In this project documentation/form_cascade (opens new window), we have multiple databases:
- car-model
- car-manufacturer
- car-types
- wheel-check
- colour
In the steps below, we will capture points representing car layer: the choices from the value relation will be filtered based on the previous field user picks. For example, if user selects Trucks as Car type (truck/car), the Car-Manufacturer field will present user with DAF Trucks, Scania or MAN. Likewise, the next drop-down menu for Car-Model will change accordingly based on the Car-Manufacturer selection.
# QGIS
To set up a the cascade form:
- Download and open documentation/form_cascade (opens new window) in QGIS
- From the layer panel, right-click on car layer and select Properties
- In the new window, select Attributes form
Notes:
- See Value Relations configuration for the following fields:
- Car-Type
- Car-Manufacturer
- Car-Model
- Colourised
- Wheel-Check
- See also Filter expressions applied to the following fields:
- Car-Manufacturer
- Car-Model
- Wheel-Check
In addition to the value relations in the survey layer, we need to set up value relation for the following non-spatial tables and the associated fields:
- manufacturer field from car-model table
- type field from car-manufacturer table
- car-type field from wheel-check table
# Mergin Maps Input
To use the cascade form in Input:
- Open Input on your device and from Projects > Explore download documentation\form_cascade
- Open the project
- Select Record and add a point
- The form will appear
- Under Survey tab, for Car-type select Car.
- Manufacturer field should short list Mercedes-Benz, Skoda and Audi. Select Audi
- For Car-Model select A8
