🔥 MSSQL on FHIR 🔥

A TypeScript library and CLI tool for loading FHIR into Microsoft SQL Server, and transpiling SQL on FHIR view definitions into T-SQL queries.

Features

SQL on FHIR compliance - Implements SQL on FHIR for transforming FHIR resources into tabular views
FHIRPath support - Full support for FHIRPath expressions in column definitions and filters
T-SQL optimisation - Generates efficient T-SQL queries using JSON_VALUE, JSON_QUERY, and OPENJSON
forEach support - Handles array flattening with CROSS APPLY for nested FHIR resources
Union support - Supports unionAll for polymorphic fields
Type casting - Automatic SQL type inference and casting based on FHIR data types
WHERE clauses - Supports view-level filtering with FHIRPath expressions
Bulk NDJSON loader - Built-in loader for importing FHIR resources from NDJSON files
Tested against SQL Server 2017, 2019, 2022 and 2025.

Quick start

The easiest way to use sof-mssql is via npx:

# Load FHIR resources from NDJSON files
npx sof-mssql load ./data --host localhost --user sa --password pass --database fhir

# Transpile a ViewDefinition from stdin to stdout
npx sof-mssql transpile <some.ViewDefinition.json >output.sql

# Or use file arguments
npx sof-mssql transpile --input some.ViewDefinition.json --output output.sql

Installation

For programmatic use, install via npm:

npm install sof-mssql

CLI usage

The CLI provides two main commands: load for bulk loading NDJSON files into SQL Server, and transpile for converting ViewDefinitions to T-SQL.

Loading NDJSON files

Bulk load FHIR resources from NDJSON files into SQL Server:

# Load all NDJSON files from a directory
npx sof-mssql load ./data \
  --host localhost \
  --user sa \
  --password yourpassword \
  --database fhir

# Load with environment variables
export MSSQL_HOST=localhost MSSQL_USER=sa MSSQL_PASSWORD=pass MSSQL_DATABASE=fhir
npx sof-mssql load ./data

# Load with custom table and batch settings
npx sof-mssql load ./data \
  --table-name my_resources \
  --batch-size 5000 \
  --parallel 2

# Preview what would be loaded
npx sof-mssql load ./data --dry-run

# Load into a native JSON column (SQL Server 2025+)
npx sof-mssql load ./data --resource-json-data-type JSON

File naming: Files must follow the pattern {ResourceType}.ndjson (e.g., Patient.ndjson, Observation.ndjson). The resource type is extracted from the filename and stored in the resource_type column.

Database options:

--host <host> - Database server hostname
--port <port> - Database server port (default: 1433)
--user <user> - Database username
--password <password> - Database password
--database <database> - Database name
--trust-server-certificate - Trust server certificate

Loading options:

--table-name <name> - Table name (default: fhir_resources)
--schema-name <name> - Schema name (default: dbo)
--resource-type <type> - Load only specific resource type
--resource-json-data-type <type> - Storage type for the json column: NVARCHAR(MAX) (default) or JSON. The JSON value uses SQL Server 2025's native JSON type and requires SQL Server 2025 or later; the value is case-insensitive. Omit the option for the default NVARCHAR(MAX) behaviour.
--truncate - Truncate table before loading
--no-create-table - Don't create table if it doesn't exist

Performance options:

--batch-size <size> - Rows per batch (default: 1000)
--parallel <count> - Parallel file processing (default: 4, use 1-2 for best reliability)

Output options:

--dry-run - Preview without loading
--verbose - Show detailed progress
--progress - Show progress bar
--quiet - Minimal output
--continue-on-error - Continue if a file fails

Transpiling ViewDefinitions

Convert SQL on FHIR ViewDefinitions to T-SQL:

# Read from stdin, write to stdout
npx sof-mssql transpile <some.ViewDefinition.json

# Read from file, write to stdout
npx sof-mssql transpile --input some.ViewDefinition.json

# Read from stdin, write to file
npx sof-mssql transpile <some.ViewDefinition.json --output query.sql

# Read from file, write to file
npx sof-mssql transpile --input some.ViewDefinition.json --output query.sql

# Fetch from remote server and transpile
curl https://example.com/fhir/ViewDefinition/1 | npx sof-mssql transpile

Options:

-i, --input <file> - Input ViewDefinition JSON file (default: stdin)
-o, --output <file> - Output SQL file (default: stdout)

Global options:

-V, --version - Output the version number
-h, --help - Display help information

Using transpiled SQL

Once you've transpiled a ViewDefinition to T-SQL, you can use it to create database views or tables.

Creating a view

Views provide a virtual table based on the query, recomputed each time the view is queried:

# Transpile ViewDefinition to SQL file
npx sof-mssql transpile --input patient_demographics.json --output patient_demographics.sql

# Connect to SQL Server and create the view
sqlcmd -S localhost -U sa -P yourpassword -d fhir -Q "
CREATE VIEW [dbo].[patient_demographics] AS
$(cat patient_demographics.sql)
"

Or directly in SQL Server Management Studio:

CREATE VIEW [dbo].[patient_demographics] AS
SELECT r.id AS [id],
  JSON_VALUE(r.json, '$.name[0].family') AS [family_name],
  CAST(JSON_VALUE(r.json, '$.birthDate') AS DATETIME2) AS [birth_date]
FROM [dbo].[fhir_resources] AS [r]
WHERE [r].[resource_type] = 'Patient'

Creating a materialised table

For better query performance, you can materialise the view results into a physical table:

-- Create and populate the table in one statement
SELECT *
INTO [dbo].[patient_demographics]
FROM (
    SELECT
    r.id AS [id], JSON_VALUE(r.json, '$.name[0].family') AS [family_name], CAST (JSON_VALUE(r.json, '$.birthDate') AS DATETIME2) AS [birth_date]
    FROM [dbo].[fhir_resources] AS [r]
    WHERE [r].[resource_type] = 'Patient'
) AS view_results

To refresh a materialised table after data changes:

-- Truncate and reload
TRUNCATE TABLE [dbo].[patient_demographics];

INSERT INTO [dbo].[patient_demographics]
SELECT r.id AS [id],
  JSON_VALUE(r.json, '$.name[0].family') AS [family_name],
  CAST(JSON_VALUE(r.json, '$.birthDate') AS DATETIME2) AS [birth_date]
FROM [dbo].[fhir_resources] AS [r]
WHERE [r].[resource_type] = 'Patient'

Programmatic usage

Basic usage

import {SqlOnFhir} from 'sof-mssql';

const sqlOnFhir = new SqlOnFhir();

Create a ViewDefinition to transpile:

{
  "resourceType": "ViewDefinition",
  "resource": "Patient",
  "name": "patient_demographics",
  "select": [
    {
      "column": [
        {
          "name": "id",
          "path": "id",
          "type": "id"
        },
        {
          "name": "family_name",
          "path": "name.family",
          "type": "string"
        },
        {
          "name": "birth_date",
          "path": "birthDate",
          "type": "date"
        }
      ]
    }
  ]
}

Transpile the ViewDefinition to T-SQL:

const result = sqlOnFhir.transpile(viewDefinition);

console.log(result.sql);

Generated SQL output:

SELECT
  r.id AS [id],
  JSON_VALUE(r.json, '$.name[0].family') AS [family_name],
  CAST(JSON_VALUE(r.json, '$.birthDate') AS DATETIME2) AS [birth_date]
FROM [dbo].[fhir_resources] AS [r]
WHERE [r].[resource_type] = 'Patient'

Access column metadata:

console.log(result.columns);

Column metadata output:

[
  { "name": "id", "type": "VARCHAR(64)", "nullable": true },
  { "name": "family_name", "type": "NVARCHAR(MAX)", "nullable": true },
  { "name": "birth_date", "type": "VARCHAR(10)", "nullable": true }
]

Custom table configuration

const sqlOnFhir = new SqlOnFhir({
  tableName: 'my_fhir_data',
  schemaName: 'clinical',
  resourceIdColumn: 'resource_id',
  resourceJsonColumn: 'resource_data'
});

Note: SqlOnFhir configures the transpiler only. The storage type of the json column - NVARCHAR(MAX) (default) or the native JSON type - is a loader concern, set with the --resource-json-data-type CLI flag or the resourceJsonDataType option of loadNdjsonFiles, not via new SqlOnFhir({ ... }). The transpiler is storage-type agnostic: the same transpiled query works over either column type, so your ViewDefinitions and transpiler configuration are unchanged for a native JSON column.

Loading into a native JSON column

The loader can store each resource in SQL Server 2025's native JSON type instead of NVARCHAR(MAX):

import { loadNdjsonFiles } from 'sof-mssql';

await loadNdjsonFiles({
  directory: './data',
  database: {
    host: 'localhost',
    user: 'sa',
    password: process.env.MSSQL_PASSWORD,
    database: 'fhir',
  },
  // "NVARCHAR(MAX)" (default) or "JSON" (SQL Server 2025+); case-insensitive.
  resourceJsonDataType: 'JSON',
});

An invalid value is rejected with a clear error before any database connection is opened. If the target table already exists with a json column that is the other supported type (NVARCHAR(MAX) when JSON was requested, or vice versa), the loader prints a warning naming both types and loads into the existing table without altering it. If the existing json column is neither NVARCHAR(MAX) nor native JSON - for example a bounded VARCHAR(100) or TEXT that cannot hold a serialised FHIR resource - the loader fails fast with an error naming the offending type, before any rows are loaded, rather than writing into a column that would truncate or corrupt the data.

Working with ViewDefinition strings

import {SqlOnFhir} from 'sof-mssql';

const sqlOnFhir = new SqlOnFhir();

// From JSON string
const viewDefJson = JSON.stringify(viewDefinition);
const result = sqlOnFhir.transpile(viewDefJson);

// From FHIR resource (with resourceType)
const fhirResource = {
  resourceType: 'ViewDefinition',
  // ... rest of ViewDefinition
};
const result2 = sqlOnFhir.transpile(fhirResource);

Type mappings and type hints

Default type mappings

By default, FHIR primitive types are mapped to the following T-SQL types:

FHIR Type	Default T-SQL Type	Rationale
`id`	`VARCHAR(64)`	ASCII-only, fixed max length
`boolean`	`BIT`	Native boolean
`integer`, `positiveint`, `unsignedint`	`INT`	32-bit integer
`integer64`	`BIGINT`	64-bit integer
`decimal`	`VARCHAR(MAX)`	Preserves arbitrary precision
`date`	`VARCHAR(10)`	Preserves partial dates (e.g., "2024-01")
`datetime`	`VARCHAR(50)`	Preserves partial datetimes and timezones
`instant`	`VARCHAR(50)`	Preserves full ISO 8601 format
`time`	`VARCHAR(20)`	Preserves partial times
`string`, `markdown`, `code`	`NVARCHAR(MAX)`	Unicode-capable text
`uri`, `url`, `canonical`	`NVARCHAR(MAX)`	Can contain Unicode (IRIs)
`uuid`	`VARCHAR(100)`	ASCII UUID format
`oid`	`VARCHAR(255)`	ASCII OID format
`base64binary`	`VARBINARY(MAX)`	Binary data

Design principle: Default mappings use VARCHAR for temporal and numeric types to preserve FHIR semantics (partial dates, arbitrary precision decimals) rather than forcing conversion to SQL native types.

Using type hints

You can override default type mappings using the tag array on column definitions. Two tag types are supported:

tsql/type - Direct T-SQL type specification:

{
  "name": "birth_date",
  "path": "birthDate",
  "type": "date",
  "tag": [
    { "name": "tsql/type", "value": "DATE" }
  ]
}

This generates a CAST expression: CAST(JSON_VALUE(r.json, '$.birthDate') AS DATE) AS [birth_date]

ansi/type - ANSI/ISO SQL standard types (automatically converted to T-SQL):

{
  "name": "age",
  "path": "age",
  "type": "integer",
  "tag": [
    { "name": "ansi/type", "value": "INTEGER" }
  ]
}

The ANSI type INTEGER is automatically converted to T-SQL INT.

{
  "name": "active",
  "path": "active",
  "type": "boolean",
  "tag": [
    { "name": "ansi/type", "value": "BOOLEAN" }
  ]
}

The ANSI type BOOLEAN is automatically converted to T-SQL BIT.

Type precedence: tsql/type > ansi/type > FHIR type defaults

Supported ANSI types:

Character: CHARACTER, CHARACTER VARYING, NATIONAL CHARACTER VARYING
Numeric: INTEGER, SMALLINT, BIGINT, DECIMAL, NUMERIC, FLOAT, REAL, DOUBLE PRECISION
Temporal: DATE, TIME, TIMESTAMP (converted to DATETIME2)
Boolean: BOOLEAN (converted to BIT)

Example with multiple columns:

This example demonstrates how different type hints affect the resulting SQL types:

{
  "resourceType": "ViewDefinition",
  "resource": "Patient",
  "select": [
    {
      "column": [
        {
          "name": "id",
          "path": "id",
          "type": "id"
        },
        {
          "name": "birth_date",
          "path": "birthDate",
          "type": "date",
          "tag": [
            { "name": "tsql/type", "value": "DATE" }
          ]
        },
        {
          "name": "deceased",
          "path": "deceasedBoolean",
          "type": "boolean",
          "tag": [
            { "name": "ansi/type", "value": "BOOLEAN" }
          ]
        }
      ]
    }
  ]
}

Type behaviour for each column:

id - Uses default FHIR type mapping: VARCHAR(64)
birth_date - Overrides default VARCHAR(10) with T-SQL DATE type
deceased - Uses ANSI BOOLEAN type, automatically converted to T-SQL BIT

Database setup

Table structure

sof-mssql expects FHIR resources to be stored in a table with the following structure:

CREATE TABLE [dbo].[fhir_resources] (
    [id] INT IDENTITY (1, 1) NOT NULL PRIMARY KEY,
    [resource_type] NVARCHAR (64) NOT NULL,
    [json] NVARCHAR (MAX) NOT NULL
);

-- Create an index on resource_type for efficient filtering by resource type
CREATE INDEX [IX_fhir_resources_resource_type]
    ON [dbo].[fhir_resources] ([resource_type]);

On SQL Server 2025 or later the json column may instead use the native JSON type for more efficient storage, with the rest of the table unchanged:

[json] JSON NOT NULL

NVARCHAR(MAX) is the default and works on SQL Server 2017+. The native JSON type is opt-in (--resource-json-data-type JSON or resourceJsonDataType: "JSON") and requires SQL Server 2025 or later. The same transpiled query SQL runs over either storage type.

The generated queries use:

resource_type column for filtering by FHIR resource type (indexed for performance)
json column containing the complete FHIR resource as JSON
SQL Server's JSON functions (JSON_VALUE, JSON_QUERY, OPENJSON) for data extraction

Performance recommendation: The index on resource_type is strongly recommended as every ViewDefinition query filters by resource type. Without this index, queries will perform full table scans.

Loading data

The easiest way to populate your database is using the built-in NDJSON loader ( see Loading NDJSON files above), which automatically creates the table with the correct structure. All FHIR resources are stored in a single table (default: fhir_resources), with the resource type extracted from the filename.

Comparing NVARCHAR(MAX) and native JSON storage

The native JSON type stores documents in a pre-parsed binary form, which Microsoft documents as roughly an 18% storage reduction; actual figures depend on the dataset. Because timings and storage are environment-dependent, this is a manual procedure rather than an automated test. To compare the two storage types for your own data on a single SQL Server 2025 instance:

Prepare a representative NDJSON dataset (for example, a few hundred megabytes of FHIR resources).

Load the same data into two separate tables, one per storage type:

npx sof-mssql load ./data --table-name fhir_nvarchar
npx sof-mssql load ./data --table-name fhir_json --resource-json-data-type JSON

Compare storage with sp_spaceused, recording data and reserved for each:

EXEC sp_spaceused 'dbo.fhir_nvarchar';
EXEC sp_spaceused 'dbo.fhir_json';

Compare read performance by running an identical transpiled ViewDefinition query against each table several times with SET STATISTICS TIME ON;, discarding the first (cold-cache) run and recording the elapsed times.
Record the dataset description, row counts, storage figures and timings.

Contributing

Contributions are welcome! Please read our CONTRIBUTING and CODE_OF_CONDUCT documents for guidelines on how to get involved.

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.claude		.claude
.github/workflows		.github/workflows
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openspec		openspec
sqlonfhir @ 70c0566		sqlonfhir @ 70c0566
src		src
.gitignore		.gitignore
.gitmodules		.gitmodules
CODE_OF_CONDUCT.md		CODE_OF_CONDUCT.md
CONTRIBUTING.md		CONTRIBUTING.md
LICENSE		LICENSE
README.md		README.md
RELEASE_CHECKLIST.md		RELEASE_CHECKLIST.md
eslint.config.cjs		eslint.config.cjs
package-lock.json		package-lock.json
package.json		package.json
skills-lock.json		skills-lock.json
tsconfig.json		tsconfig.json
vitest.config.ts		vitest.config.ts

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🔥 MSSQL on FHIR 🔥

Features

Quick start

Installation

CLI usage

Loading NDJSON files

Transpiling ViewDefinitions

Using transpiled SQL

Creating a view

Creating a materialised table

Programmatic usage

Basic usage

Custom table configuration

Loading into a native JSON column

Working with ViewDefinition strings

Type mappings and type hints

Default type mappings

Using type hints

Database setup

Table structure

Loading data

Comparing NVARCHAR(MAX) and native JSON storage

Contributing

License

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🔥 MSSQL on FHIR 🔥

Features

Quick start

Installation

CLI usage

Loading NDJSON files

Transpiling ViewDefinitions

Using transpiled SQL

Creating a view

Creating a materialised table

Programmatic usage

Basic usage

Custom table configuration

Loading into a native JSON column

Working with ViewDefinition strings

Type mappings and type hints

Default type mappings

Using type hints

Database setup

Table structure

Loading data

Comparing NVARCHAR(MAX) and native JSON storage

Contributing

License

About

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