Create database index with Entity Framework

问题:

Say I have the following model:

[Table("Record")]
public class RecordModel
{
    [Key]
    [DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
    [Display(Name = "Record Id")]
    public int RecordId { get; set; }

    [StringLength(150)]
    public string Name { get; set; }

    [Required]
    [StringLength(15)]
    public string IMEI { get; set; }
}

Is it possible to add an index to the IMEI column through using an attribute, data annotation, or something from the model?

回答1:

According to this link: Creating Indexes via Data Annotations with Entity Framework 5.0 you should write some kind of extension code:

using System; 

[AttributeUsage(AttributeTargets.Property, Inherited = false, AllowMultiple = true)]
public class IndexAttribute : Attribute
{
    public IndexAttribute(string name, bool unique = false)
    {
        this.Name = name;
        this.IsUnique = unique;
    }

    public string Name { get; private set; }

    public bool IsUnique { get; private set; }
}

and the second class:

using System.ComponentModel.DataAnnotations.Schema;
using System.Data.Entity;
using System.Linq;
using System.Reflection;

public class IndexInitializer<T> : IDatabaseInitializer<T> where T : DbContext
{
    private const string CreateIndexQueryTemplate = "CREATE {unique} INDEX {indexName} ON {tableName} ({columnName})";

    public void InitializeDatabase(T context)
    {
        const BindingFlags PublicInstance = BindingFlags.Public | BindingFlags.Instance;

        foreach (var dataSetProperty in typeof(T).GetProperties(PublicInstance).Where(
            p => p.PropertyType.Name == typeof(DbSet<>).Name))
        {
            var entityType = dataSetProperty.PropertyType.GetGenericArguments().Single();

            TableAttribute[] tableAttributes = (TableAttribute[])entityType.GetCustomAttributes(typeof(TableAttribute), false);

            foreach (var property in entityType.GetProperties(PublicInstance))
            {
                IndexAttribute[] indexAttributes = (IndexAttribute[])property.GetCustomAttributes(typeof(IndexAttribute), false);
                NotMappedAttribute[] notMappedAttributes = (NotMappedAttribute[])property.GetCustomAttributes(typeof(NotMappedAttribute), false);
                if (indexAttributes.Length > 0 && notMappedAttributes.Length == 0)
                {
                    ColumnAttribute[] columnAttributes = (ColumnAttribute[])property.GetCustomAttributes(typeof(ColumnAttribute), false);

                    foreach (var indexAttribute in indexAttributes)
                    {
                        string indexName = indexAttribute.Name;
                        string tableName = tableAttributes.Length != 0 ? tableAttributes[0].Name : dataSetProperty.Name;
                        string columnName = columnAttributes.Length != 0 ? columnAttributes[0].Name : property.Name;
                        string query = CreateIndexQueryTemplate.Replace("{indexName}", indexName)
                            .Replace("{tableName}", tableName)
                            .Replace("{columnName}", columnName)
                            .Replace("{unique}", indexAttribute.IsUnique ? "UNIQUE" : string.Empty);

                        context.Database.CreateIfNotExists();

                        context.Database.ExecuteSqlCommand(query);
                    }
                }
            }
        }
    }
}

After it you can use your index this way:

[Required]
[Index("IMEIIndex", unique: true)]
[StringLength(15)]
public string IMEI { get; set; }

回答2:

UPDATE: Since the release of EF 6.1. (March 17th, 2014) there is indeed an [Index] attribute available.

Functionality as:

[Index("IMEIIndex", IsUnique = true)]
public string IMEI { get; set; }

comes out of the box.

PS: other properties are Order and IsClustered.

---

According to this link: http://blogs.msdn.com/b/adonet/archive/2014/02/11/ef-6-1-0-beta-1-available.aspx

It will be available in EF 6.1 as a standard DataAnnotation attribute.

IndexAttribute allows indexes to be specified by placing an [Index] attribute on a property (or properties) in your Code First model. Code First will then create a corresponding index in the database.