Adding same entity object more than once with EF Core

Question

In below code , I want to add myEntity object more than once to database using EF Core. but each time with different value on property id but all other properties are the same. How can I do this? because it's only adding 1 row in the database.

I want to do this because I don't want to repeat calling GetCurrentLocalDateTime() for each iteration and also in the else statement.

 var myEntity = _mapper.Map<AEntity >(entityDto);

     myEntity.updatedAt = _helper.GetCurrentLocalDateTime();
     myEntity.CreatedAt = _helper.GetCurrentLocalDateTime();
           

            if (entityDto.ids != null || entityDto.ids.Count > 0)
            {
                foreach (var id in entityDto.ids)
                {
                    myEntity.id = id;
                    await _dbContext.myEntities.AddAsync(myEntity);
                }
            }
           
            else
            {
                await _dbContext.myEntities.AddAsync(myEntity);
            }


            await _dbContext.SaveChangesAsync();

Richard Deeming · Accepted Answer · 2022-01-13 14:48:41Z

You can't add a single instance of a class, change one of its properties, and add it again expecting a new instance to be added to your database. All that will happen is that you change the property of the single instance you have added.

Instead, you will need to map the DTO multiple times, so that you add multiple instance of your entity class to the DbSet.

You also need to use && instead of || in your if condition. Use OR (||) will result in a NullReferenceException if the entityDto.ids collection is null.

var now = _helper.GetCurrentLocalDateTime();
if (entityDto.ids != null && entityDto.ids.Count > 0)
{
    foreach (var id in entityDto.ids)
    {
        var myEntity = _mapper.Map<AEntity>(entityDto);
        myEntity.updatedAt = now;
        myEntity.CreatedAt = now;
        myEntity.id = id;
        await _dbContext.myEntities.AddAsync(myEntity);
    }
}
else
{
    var myEntity = _mapper.Map<AEntity>(entityDto);
    myEntity.updatedAt = now;
    myEntity.CreatedAt = now;
    await _dbContext.myEntities.AddAsync(myEntity);
}

await _dbContext.SaveChangesAsync();

B_Cbk · Accepted Answer · 2022-01-13 14:35:40Z

0

It uses it to add multiple data.Look at these

.AddRangeAsync() .AddRange()

you can try to keep your data in list and save it all at once with "addrange()"

answered Jan 13, 2022 at 14:35

B_Cbk

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Comments

Steve Py · Accepted Answer · 2022-01-13 20:57:25Z

Yes, it is possible, though I would use caution to ensure that this is only to insert a number of copies:

            foreach (var id in entityDto.ids)
            {
                myEntity.id = id;
                await _dbContext.myEntities.AddAsync(myEntity);
                _dbContext.Entry(myEntity).State = EntityState.Detached;
            }

By detaching the entity, the DbContext will no longer be tracking it, so updating it and adding it again will be treated as a request to add a new entity.

Normally this kind of code results in a bug where developers are trying to reuse a single entity instance to update multiple data rows. This is a rather odd requirement to insert several copies of the same data, so I would ensure it is documented well so future developers don't try repurposing it. :)

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