BulkMerge

This method merges all rows from the client application into the database in bulk — inserting new rows and updating existing ones based on the defined qualifiers. It is supported for Db2.

This page documents the Db2-specific arguments and examples. For the SQL Server implementation, see BulkMerge (SQL Server).

Call Flow Diagram

The diagram below shows the flow when calling this operation.

flowchart TD
    Client["Client<br/>(RepoDB)"] -->|BulkMerge| Source["Entities /<br/>DataTable /<br/>DbDataReader"]
    Source --> Pseudo["Create Pseudo Table<br/>(Physical)"]
    Pseudo --> BulkCopy["DB2BulkCopy"]
    BulkCopy -->|Write| PseudoTable[("Pseudo Table")]
    PseudoTable --> Decision{"identityBehavior ==<br/>ReturnIdentity?"}
    Decision -->|NO| Merge["MERGE INTO ... USING ...<br/>WHEN MATCHED THEN UPDATE<br/>WHEN NOT MATCHED THEN INSERT"]
    Merge --> Table[("Target Table")]
    Decision -->|YES| Snapshot["LEFT JOIN snapshot:<br/>classify matched vs. unmatched rows"]
    Snapshot --> UpdateStep["MERGE ... WHEN MATCHED<br/>THEN UPDATE (matched rows only)"]
    Snapshot --> InsertStep["SELECT id FROM FINAL TABLE(<br/>INSERT ... unmatched rows only)"]
    UpdateStep --> Table
    InsertStep --> Table
    InsertStep -->|"assign identities<br/>back to entities"| Client
    PseudoTable -->|Drop| Cleanup(["Pseudo Table Dropped"])

Use Case

Use this method to merge rows at high speed. It leverages the native bulk operation from the IBM Data Server .NET Provider via the DB2BulkCopy class.

For merging 1,000 or more rows, prefer this method over MergeAll.

A pseudo (staging) table is created under a transaction context. The library writes to it via BulkInsert internally, then cascades the changes to the target table via a MERGE statement — see Operations (Db2) for the underlying mechanics.

Special Arguments

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

qualifiers defines the fields used to match existing rows, corresponding to the WHERE clause. Defaults to the primary column if not specified.

mappings (via Db2BulkInsertMapItem) defines explicit column mappings between the source properties and the destination columns, with an optional DB2Type override per mapping. 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 Db2BulkImportIdentityBehavior) controls whether newly generated identity values are set back on the data entities. Disabled (KeepIdentity) by default.

pseudoTableType (via Db2BulkImportPseudoTableType) controls the kind of staging table used internally.

Every pseudoTableType value currently resolves to Physical at runtime — see Operations (Db2) for details.

The identity column, if any, is always left out of the INSERT column list generated for unmatched rows — a brand-new row’s identity property is typically an unset default (e.g. 0), not a real value meant to be inserted as-is.

Identity Setting Alignment

When identityBehavior is ReturnIdentity, a single atomic MERGE cannot both branch on match and read back generated identities in Db2. The library instead runs three separate statements:

1. A LEFT JOIN snapshot between the staging and target table (ordered by a __RepoDbBulkRowOrder__ identity column added to the staging table) to classify each staged row as matched or unmatched.
2. A MERGE ... WHEN MATCHED THEN UPDATE for the matched rows only (skipped entirely if nothing matched).
3. An insert-only statement — again via SELECT identity FROM FINAL TABLE (INSERT ...) — for the unmatched rows, reading back their new identities.

This is not atomic — three round-trips instead of one — and the matched/unmatched classification from step 1 can go stale if another connection modifies the target table before steps 2 and 3 run.

Usability

Given a list of Person models containing both existing and new rows, the following example bulk-merges them into the Person table.

using (var connection = new DB2Connection(connectionString))
{
    var mergedRows = connection.BulkMerge(people);
}

To specify a batch size:

using (var connection = new DB2Connection(connectionString))
{
    var mergedRows = connection.BulkMerge(people, batchSize: 100);
}

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

DataTable

using (var connection = new DB2Connection(connectionString))
{
    var table = ConvertToDataTable(people);
    var mergedRows = connection.BulkMerge("Person", table);
}

Dictionary/ExpandoObject

using (var sourceConnection = new DB2Connection(sourceConnectionString))
{
    var result = sourceConnection.QueryAll("Person");
    using (var destinationConnection = new DB2Connection(destinationConnectionString))
    {
        var mergedRows = destinationConnection.BulkMerge("Person", result,
            qualifiers: Field.From("LastName", "DateOfBirth"));
    }
}

DataReader

using (var sourceConnection = new DB2Connection(sourceConnectionString))
{
    using (var reader = sourceConnection.ExecuteReader("SELECT * FROM Person WHERE (IsActive = 1)"))
    {
        using (var destinationConnection = new DB2Connection(destinationConnectionString))
        {
            var rows = destinationConnection.BulkMerge("Person", reader);
        }
    }
}

To bulk-merge via DataEntityDataReader:

using (var connection = new DB2Connection(connectionString))
{
    var people = GetPeople(10000);
    using (var reader = new DataEntityDataReader<Person>(people))
    {
        var mergedRows = connection.BulkMerge("Person", reader);
    }
}

Field Qualifiers

By default, the primary column is used as the qualifier. To override, pass a list of Field objects in the qualifiers argument.

using (var connection = new DB2Connection(connectionString))
{
    var people = GetPeople(10000);
    var mergedRows = connection.BulkMerge<Person>(people,
        qualifiers: e => new { e.LastName, e.DateOfBirth });
}

Use indexed columns from the target table as qualifiers to maximize performance.

Column Mappings

Add column mappings using the Db2BulkInsertMapItem class.

var mappings = new List<Db2BulkInsertMapItem>();

// Add the mappings
mappings.Add(new Db2BulkInsertMapItem("SourceId", "DestinationId"));
mappings.Add(new Db2BulkInsertMapItem("SourceName", "DestinationName"));
mappings.Add(new Db2BulkInsertMapItem("SourceIsActive", "DestinationIsActive"));
mappings.Add(new Db2BulkInsertMapItem("SourceDateInsertedUtc", "DestinationDateInsertedUtc"));

// Execute
using (var connection = new DB2Connection(connectionString))
{
    var people = GetPeople(10000);
    var mergedRows = connection.BulkMerge(people,
        mappings: mappings);
}

Targeting a Table

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

using (var connection = new DB2Connection(connectionString))
{
    var people = GetPeople(10000);
    var mergedRows = connection.BulkMerge("Person", people);
}

Async Method

An equivalent BulkMergeAsync method is also available.

using (var connection = new DB2Connection(connectionString))
{
    var mergedRows = await connection.BulkMergeAsync(people);
}