Operations · 4 min read

BulkInsert

This method inserts all rows from the client application into the database in bulk. It is supported for DuckDB.

Call Flow Diagram

The diagram below shows the flow when calling this operation.

flowchart TD
    Client["Client<br/>(RepoDB)"] -->|BulkInsert| Source["Entities /<br/>DataTable /<br/>DbDataReader"]
    Source --> Decision{"identityBehavior ==<br/>ReturnIdentity?"}
    Decision -->|NO| Direct["DuckDbBulkAppender"]
    Direct -->|Write| Table[("Target Table")]
    Decision -->|YES| Pseudo["Create Pseudo Table<br/>(TEMP by default)"]
    Pseudo --> Staged["DuckDbBulkAppender"]
    Staged -->|Write| PseudoTable[("Pseudo Table")]
    PseudoTable --> Insert["INSERT INTO ... SELECT ...<br/>FROM Pseudo ORDER BY rowid<br/>RETURNING identity"]
    Insert --> Table
    Insert -->|"assign identities<br/>back to entities"| Client
    PseudoTable -->|Drop| Cleanup(["Pseudo Table Dropped"])

Use Case

Use this method to insert rows at high speed. It leverages DuckDB.NET’s native DuckDBAppender via the DuckDbBulkAppender wrapper.

For inserting 1,000 or more rows, prefer this method over InsertAll.

Rows are written straight to the target table. A staging table is only used when identityBehavior is set to ReturnIdentity (see below) — see Operations (DuckDB) for the underlying mechanics.

Special Arguments

The mappings, bulkCopyTimeout, batchSize, identityBehavior and pseudoTableType arguments are available for this operation.

mappings (via DuckDbBulkInsertMapItem) defines explicit column mappings between the source properties and the destination columns. When omitted, columns are auto-mapped by name (case-insensitive).

bulkCopyTimeout overrides the command timeout, in seconds.

batchSize overrides the number of rows sent to the server per batch. When not set, all items are sent at once.

identityBehavior (via DuckDbBulkImportIdentityBehavior) controls whether newly generated identity values are set back on the data entities. Disabled (KeepIdentity) by default. Enabling this (ReturnIdentity) routes the operation through a staging table instead, reading the generated identity values back via a RETURNING clause appended to the same INSERT statement.

pseudoTableType (via DuckDbBulkImportPseudoTableType) controls the kind of staging table used when identityBehavior is ReturnIdentity.

Auto currently behaves exactly like Memory (a TEMP table) — see Operations (DuckDB) for details.

The DbDataReader overload has no identityBehavior argument — a forward-only, single-pass reader cannot be rewound to correlate generated identity values back onto a source row, so ReturnIdentity is not supported for that overload.

Identity Setting Alignment

When identityBehavior is ReturnIdentity, the library relies on the pseudo table’s own rowid pseudocolumn to track each entity’s position in the source IEnumerable — no extra tracking column is added. The staged rows are then fed into the real INSERT ordered by rowid, and the generated identities are read back — in the same statement — via RETURNING identity, then assigned back to the correct entity by that row order.

Usability

The following example defines a method that produces a list of Person objects, then bulk-inserts 10,000 rows into the Person table.

private IEnumerable<Person> GetPeople(int count = 1000)
{
    for (var i = 0; i < count; i++)
    {
        yield return new Person
        {
            Name = $"Person-{i}",
            IsActive = true,
            CreatedDateUtc = DateTime.UtcNow
        };
    }
}

using (var connection = new DuckDBConnection(ConnectionString))
{
    var people = GetPeople(10000);
    var insertedRows = connection.BulkInsert(people);
}

To specify a batch size:

using (var connection = new DuckDBConnection(ConnectionString))
{
    var people = GetPeople(10000);
    var insertedRows = connection.BulkInsert(people, batchSize: 100);
}

When batchSize is not set, all rows are sent to the server in a single batch.

To return the newly generated identity values:

using (var connection = new DuckDBConnection(ConnectionString))
{
    var people = GetPeople(10000);
    var insertedRows = connection.BulkInsert(people,
        identityBehavior: DuckDbBulkImportIdentityBehavior.ReturnIdentity);
}

DataTable

using (var connection = new DuckDBConnection(ConnectionString))
{
    var people = GetPeople(10000);
    var table = ConvertToDataTable(people);
    var insertedRows = connection.BulkInsert("Person", table);
}

Dictionary/ExpandoObject

using (var sourceConnection = new DuckDBConnection(sourceConnectionString))
{
    var result = sourceConnection.QueryAll("Person");
    using (var destinationConnection = new DuckDBConnection(destinationConnectionString))
    {
        var insertedRows = destinationConnection.BulkInsert("Person", result);
    }
}

DataReader

using (var sourceConnection = new DuckDBConnection(sourceConnectionString))
{
    using (var reader = sourceConnection.ExecuteReader("SELECT * FROM \"Person\";"))
    {
        using (var destinationConnection = new DuckDBConnection(destinationConnectionString))
        {
            var rows = destinationConnection.BulkInsert("Person", reader);
        }
    }
}

To bulk-insert via DataEntityDataReader:

using (var connection = new DuckDBConnection(ConnectionString))
{
    var people = GetPeople(10000);
    using (var reader = new DataEntityDataReader<Person>(people))
    {
        var insertedRows = connection.BulkInsert("Person", reader);
    }
}

Column Mappings

Add column mappings using the DuckDbBulkInsertMapItem class.

var mappings = new List<DuckDbBulkInsertMapItem>();

// Add the mappings
mappings.Add(new DuckDbBulkInsertMapItem("SourceId", "DestinationId"));
mappings.Add(new DuckDbBulkInsertMapItem("SourceName", "DestinationName"));
mappings.Add(new DuckDbBulkInsertMapItem("SourceIsActive", "DestinationIsActive"));

// Execute
using (var connection = new DuckDBConnection(ConnectionString))
{
    var people = GetPeople(10000);
    var insertedRows = connection.BulkInsert(people,
        mappings: mappings);
}

Targeting a Table

To target a specific table, pass the literal table name.

using (var connection = new DuckDBConnection(ConnectionString))
{
    var people = GetPeople(10000);
    var insertedRows = connection.BulkInsert("Person", people);
}

Async Method

An equivalent BulkInsertAsync method is also available.

using (var connection = new DuckDBConnection(ConnectionString))
{
    var people = GetPeople(10000);
    var insertedRows = await connection.BulkInsertAsync(people);
}