Configure Merge View

By default, the merge UI displays a fixed set of patient fields (ID, name, gender, birth date). The MergeViewModel feature lets you customize which fields appear in the merge view — and in what order — without changing any code.

A MergeViewModel is a database record containing an ordered list of field descriptors. Each field has a human-readable label and a JSONPath expression that tells the system how to read and write values from FHIR Patient resources.

How it works

1. You create a MergeViewModel record in the database with the desired field configuration.
2. You set the MERGE_VIEW_MODEL_ID environment variable to the record's ID.
3. When a clinician opens the merge UI, the system loads the configured fields and renders them instead of the defaults.

If the environment variable is not set or the record is not found, the system falls back to the default field list automatically.

Environment variable

Create a MergeViewModel

Insert a record directly into the database:

INSERT INTO mpi.mergeviewmodel (id, version, resource)
VALUES (
  'my-merge-view',
  1,
  '{
    "id": "my-merge-view",
    "name": "Custom Merge View",
    "fields": [
      { "label": "ID",          "path": "$.id" },
      { "label": "First Name",  "path": "$.name[0].given[0]" },
      { "label": "Last Name",   "path": "$.name[0].family" },
      { "label": "Gender",      "path": "$.gender" },
      { "label": "Birth Date",  "path": "$.birthDate" },
      { "label": "Phone",       "path": "$.telecom[?(@.system==\"phone\")].value" },
      { "label": "Email",       "path": "$.telecom[?(@.system==\"email\")].value" }
    ]
  }'::jsonb
);

Then set the environment variable for the MDM frontend service:

MERGE_VIEW_MODEL_ID=my-merge-view

After restarting the service, the merge UI will display the configured fields.

Field descriptor format

Each entry in the fields array has two properties:

The same JSONPath expression is used for both reading the value from each patient and writing the selected value into the merge result. The order of fields in the array determines the display order in the UI.

Supported JSONPath expressions

Field paths use JSONPath syntax compatible with the jsonpath-plus library. Examples:

Default fields

When no MergeViewModel is configured, the system uses the following default fields:

Merge UI behavior

The merge view displays each configured field as a row with values from both patient records:

• If both patients have the same value for a field, it is displayed without a selection control.
• If the values differ, radio buttons allow the clinician to pick which value to keep in the merged result.
• If a JSONPath expression resolves to no value in one or both patients, an empty string is shown.

The clinician can also select an entire patient column at once using the header radio buttons, which copies all field values from that patient into the merge result.

Update a MergeViewModel

To change the field configuration, update the record in the database:

UPDATE mpi.mergeviewmodel
SET resource = '{
  "id": "my-merge-view",
  "name": "Updated Merge View",
  "fields": [
    { "label": "ID",          "path": "$.id" },
    { "label": "First Name",  "path": "$.name[0].given[0]" },
    { "label": "Last Name",   "path": "$.name[0].family" },
    { "label": "Birth Date",  "path": "$.birthDate" }
  ]
}'::jsonb,
version = version + 1
WHERE id = 'my-merge-view';

Changes take effect on the next merge page load — no redeployment is required.

Database schema

The MergeViewModel is stored in two tables:

mpi.mergeviewmodel — active configuration:

mpi.mergeviewmodel_history — audit trail of previous versions: