Code-first migration: How to set default value for new property?

问题

I am using EF6 for storing instances of the report class in my database. The database already contains data. Say I wanted to add a property to report,

public class report {
    // ... some previous properties

    // ... new property:
    public string newProperty{ get; set; }
}

Now if I go to the package-manager console and execute

add-migration Report-added-newProperty
update-database

I will get a file in the '/Migrations' folder adding a newProperty column to the table. This works fine. However, on the older entries in the database, the value for the newProperty is now an empty string. But I want it to be, e.g., "old".

So my question is: How do I set default values for new properties (of any type) in the migration script (or elsewhere)?

回答1:

If you see the generated migration code you will see AddColumn

AddColumn("dbo.report", "newProperty", c => c.String(nullable: false));

You can add defaultValue

AddColumn("dbo.report", "newProperty", 
           c => c.String(nullable: false, defaultValue: "old"));

Or add defaultValueSql

AddColumn("dbo.report", "newProperty",
           c => c.String(nullable: false, defaultValueSql: "GETDATE()"));

回答2:

You have to change the line in your migration script which adds the the property/column like this:

AddColumn("dbo.reports", "newProperty", c => c.String(nullable: false, defaultValue: "test"));

回答3:

Hope it helps someone. Putting everything together from previous answers (example using a boolean property):

1) Add a new property to the entity.

/// <summary>
/// Determines if user is enabled or not. Default value is true
/// </summary>
public bool IsEnabled { get; set; }

2) Run the command below to add the new change in the migrations.

add-migration addIsEnabledColumn

3) A migration file is created from the command above, open that file.

4) Set the default value.

public override void Up()
    {
        AddColumn("dbo.AspNetUsers", "IsEnabled", c => c.Boolean(nullable: false, defaultValue: true));
    }

回答4:

I have resolved this problem by overriding the SaveChanges method. See below for my solution.

Solution Explain

i) Override the SaveChanges method in the DbContext class.

public override int SaveChanges()
{
    return base.SaveChanges();
}

ii) Write logic to set default values

public override int SaveChanges()
{
    //set default value for your property
    foreach (var entry in ChangeTracker.Entries().Where(entry => entry.Entity.GetType().GetProperty("YOUR_PROPERTY") != null))
    {
        if (entry.State == EntityState.Added)
        {
            if (entry.Property("YOUR_PROPERTY").CurrentValue == null)
                entry.Property("YOUR_PROPERTY").CurrentValue = YOUR_DEFAULT_VALUE;
        }
    }

    return base.SaveChanges();
}

Example

public override int SaveChanges()
{
    //set default value for RegistedDate property
    foreach (var entry in ChangeTracker.Entries().Where(entry => entry.Entity.GetType().GetProperty("RegistedDate") != null))
    {
        if (entry.State == EntityState.Added)
        {
            if ((DateTime)entry.Property("RegistedDate").CurrentValue == DateTime.MinValue)
                entry.Property("RegistedDate").CurrentValue = DateTime.Now;
        }
    }

    //set default value for IsActive property
    foreach (var entry in ChangeTracker.Entries().Where(entry => entry.Entity.GetType().GetProperty("IsActive") != null))
    {
        if (entry.State == EntityState.Added)
        {
            if(entry.Property("IsActive").CurrentValue == null)
                entry.Property("IsActive").CurrentValue = false;
        }
    }

    return base.SaveChanges();
}

回答5:

I found that just using Auto-Property Initializer on entity property is enough to get the job done.

For example:

public class Thing {
    public bool IsBigThing { get; set; } = false;
}

来源：https://stackoverflow.com/questions/31025967/code-first-migration-how-to-set-default-value-for-new-property

标签

.net

entity-framework

entity-framework-6

ef-migrations