Bulk Merge

Definition

MERGE all entities from the database.

A merge is an UPSERT operation. All rows that match the entity key are considered as existing and are UPDATED, other rows are considered as new rows and are INSERTED in the database.

// Easy to use
ctx.BulkMerge(list);

// Easy to customize
context.BulkMerge(customers, options => options.ColumnPrimaryKeyExpression = customer => customer.Code);

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Purpose

Merging entities using a custom key from file importation is a typical scenario.

Despite the ChangeTracker being outstanding to track what's modified, it lacks in term of scalability and flexibility.

SaveChanges requires one database round-trip for every entity to insert or update. So if you need to insert or update 10000 entities, then 10000 database round-trips will be performed which is INSANELY slow.

BulkMerge in counterpart offers great customization and requires the minimum database round-trips as possible.

Performance Comparisons

Operations 1,000 Entities 2,000 Entities 5,000 Entities
SaveChanges 1,000 ms 2,000 ms 5,000 ms
BulkMerge 65 ms 80 ms 110 ms
## FAQ

How can I specify more than one option?

You can specify more than one option using anonymous block.

context.BulkMerge(list, options => {
	options.BatchSize = 100;
	options.ColumnInputExpression = c => new {c.ID, c.Name, c.Description};
});

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How can I specify the Batch Size?

You can specify a custom batch size using the BatchSize option.

Read more: BatchSize

context.BulkMerge(list, options => options.BatchSize = 100);

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How can I specify custom columns to Merge?

You can specify custom columns using the ColumnInputExpression option.

Read more: ColumnInputExpression

context.BulkMerge(list, options => options.ColumnInputExpression = c => new {c.Name, c.Description});

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How can I specify custom columns to exclude on insert or update?

You can specify custom columns to exclude using the IgnoreOnMergeInsertExpression and IgnoreOnMergeUpdateExpression option.

Read more: IgnoreOnMergeInsertExpression

Read more: IgnoreOnMergeUpdateExpression

context.BulkMerge(list, options =>
	{
		options.IgnoreOnMergeInsertExpression = customer => new { customer.UpdatedDate, customer.UpdatedUser };
		options.IgnoreOnMergeUpdateExpression = customer => customer.Code, customer.Col2;
	});

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How can I specify custom keys to use?

You can specify custom keys using the ColumnPrimaryKeyExpression option.

Read more: ColumnPrimaryKeyExpression

// Single Key
context.BulkMerge(customers, options => options.ColumnPrimaryKeyExpression = customer => customer.Code);

// Surrogate Key
context.BulkMerge(customers, options => options.ColumnPrimaryKeyExpression = customer => new { customer.Code1, customer.Code2 });

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How can I include child entities (Entity Graph)?

You can include child entities using the IncludeGraph option. Make sure to read about the IncludeGraph since this option is not as trivial as others.

Read more: IncludeGraph

context.BulkMerge(list, options => options.IncludeGraph = true);

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Why BulkMerge doesn't use the ChangeTracker?

To provide the best performance possible!

Since using the ChangeTracker can greatly reduce performance, we chose to let BulkSaveChanges method handle scenarios with ChangeTracker and BulkMerge, scenarios without it.