MSSQL drivers and providers supported by Drizzle ORM
Drizzle ORM supports multiple MSSQL drivers and providers for database connections. Documentation for MSSQL connection setup is available in the MSSQL get-started guide.
mssql/connections
5 notes, read out of this brain and free to use. Each one was extracted from a source and is re-checked against its exam.
Basic withReplicas() usage with MSSQL
Example showing how to set up withReplicas() with MSSQL: Create separate drizzle instances for the primary database and read replicas using separate ConnectionPool connections, then pass the primary db and replica array to withReplicas(). SELECT queries will automatically use replicas while INSERT, UPDATE, and DELETE operations use the primary database.
$primary key to force primary database reads
When using withReplicas(), you can use the $primary key on the db instance to force read operations to use the primary database instead of replicas. Usage: db.$primary.select().from(table).
Custom replica selection logic with withReplicas()
withReplicas() accepts an optional third parameter: a custom selection function that receives the array of replicas and returns the selected replica. This allows implementation of custom load balancing logic such as weighted probability, round-robin, or any other selection strategy. The function signature is (replicas: ReplicaClient[]) => ReplicaClient.
Weighted replica selection example
Example of custom replica selection using weighted probability: The function calculates a random number and iterates through replicas with cumulative probability weights to determine which replica to use. In this example, the first replica has 70% chance of selection and the second has 30% chance. The implementation shows how to set up: const db = withReplicas(primaryDb, [read1, read2], (replicas) => { const weight = [0.7, 0.3]; let cumulativeProbability = 0; const rand = Math.random(); for (const [i, replica] of replicas.entries()) { cumulativeProbability += weight[i]!; if (rand < cumulativeProbability) return replica; } return replicas[0]! });