实体框架如果不存在则添加而不更新

Question

I like the fact that AddOrUpdate let's you specify a filter to check to avoid adding duplicates. But I would like similar functionality without the update.

Right now I do something like this:

var checkProfile = from p in db.Profile
    where p => p.LastName == newProfile.lastName
         && p => p.FirstName == newProfile.firstName
         && p => p.Middle== newProfile.middle
    select p;
if (checkProfile.FirstOrDefault() == null)
{
    db.Profile.Add(newProfile);
    db.SaveChanges();
}

I know I can do something like this:

db.Profile.AddOrUpdate(p => new {p.LastName, p.FirstName, p.Middle}, newProfile);
db.SaveChanges();

But I would rather skip modifying the data in this case.

The first example does what I want but with more code. Is there a simpler/cleaner way to do what I want in the first example?

Update:

I like Ognyan Dimitrov's suggestion. I'm trying to implement it. My models inherit from BaseEntity. Can I put a generic version of that there?

My model is defined:

public class Address :BaseEntity
{

My BaseEntity:

public class BaseEntity 
{
    public virtual T AddIfNotExists<T>(T entity, Expression<Func<T, bool>> predicate = null)
    {
        var exists = predicate != null ? DbSet.Any(predicate) : DbSet.Any();
        return !exists ? DbSet.Add(entity) : null;
    }
}

I'm getting errors for Any(...) and Add(...). The error for Add(...) is 'An object reference is required for the non-static field, method, or property 'System.Data.Entity.DbSet.Add(object)' '

Should I be using this.Add(object) ?

Update 2:

I've created this code:

public static class DbSetExtensions
{
    public static T AddIfNotExists<T>(this DbSet<T> dbSet, T entity, Expression<Func<T, bool>> predicate = null) where T : class, new()
    {
        var exists = predicate != null ? dbSet.Any(predicate) : dbSet.Any();
        return !exists ? dbSet.Add(entity) : null;
    }

}

Now I'm trying to call it like this, but it's not correct. Forgive my lack of understanding.

_db.ProfileIdentifier.AddIfNotExists(newIdentifier,
            pi => new {pi.ProfileId, pi.ProfileIdentifierTypeId, pi.ProfileIdentifierValue});

Update - Solution:

I can call the DbSetextensions like this:

_db.ProfileIdentifier.AddIfNotExists(newIdentifier,
            pi => pi.ProfileId == profileId &&  
            pi.ProfileIdentifierTypeId == (int)type &&  
            pi.ProfileIdentifierValue == value);

Thanks a lot for working with me Ognyan!!!

Answer 1

Have you tried to check if the entity exists and if not - add it? Like this :

UPDATE

using System.Linq.Expressions;
    public class ContextWithExtensionExample
    {
        public void DoSomeContextWork(DbContext context)
        {
            var uni = new Unicorn();
            context.Set<Unicorn>().AddIfNotExists(uni , x => x.Name == "James");
        }
    }

    public static class DbSetExtensions
    {
        public static T AddIfNotExists<T>(this DbSet<T> dbSet, T entity, Expression<Func<T, bool>> predicate = null) where T : class, new()
        {
            var exists = predicate != null ? dbSet.Any(predicate) : dbSet.Any();
            return !exists ? dbSet.Add(entity) : null;
        }
    }

You can use this method directly and remember to call DbContext.SaveChanges() after the call.

Answer 2

All the other answers are incorrect.

"Read before write" can violate data integrity without being put inside a transaction control.

In SQL Server, you can use merge statement. However merge statement is not available in EF.

Answer 3

The solution is OK, when you have to add just one item, but it's very expensive in terms of performance in case you have to add multiple items. I think there is a better solution:

public static class DbSetExtensions
{
    public static EntityEntry<TEnt> AddIfNotExists<TEnt, TKey>(this DbSet<TEnt> dbSet, TEnt entity, Func<TEnt, TKey> predicate) where TEnt : class
    {
        var exists = dbSet.Any(c => predicate(entity).Equals(predicate(c)));
        return exists
            ? null
            : dbSet.Add(entity);
    }

    public static void AddRangeIfNotExists<TEnt, TKey>(this DbSet<TEnt> dbSet, IEnumerable<TEnt> entities, Func<TEnt, TKey> predicate) where TEnt : class
    {
        var entitiesExist = from ent in dbSet
            where entities.Any(add => predicate(ent).Equals(predicate(add)))
            select ent;

        dbSet.AddRange(entities.Except(entitiesExist));
    }
}

So later it can be used like this:

using (var context = new MyDbContext())
{
    var user1 = new User { Name = "Peter", Age = 32 };
    context.Users.AddIfNotExists(user1, u => u.Name);

    var user2 = new User { Name = "Joe", Age = 25 };
    context.Users.AddIfNotExists(user2, u => u.Age);

    // Adds user1 if there is no user with name "Peter"
    // Adds user2 if there is no user with age 25
    context.SaveChanges();
}

Answer 4

I used something like, read these two posts to make my code. I hope to help those in need of a similar signature to AddOrUpdate.

Entity Framework Add if not exist without update

Making AddOrUpdate change only some properties

using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;

namespace System.Data.Entity.Migrations
{
    //
    // Summary:
    //     Metodos de extensão para System.Data.Entity.IDbSet
    public static class DbSetMigrationsGustavoExtensions
    {
        /// <summary>
        /// Adiciona uma entidade se ela não existe ainda
        /// Assinatura semelhante ao AddOrUpdate
        /// </summary>
        /// <typeparam name="TEntity"></typeparam>
        /// <param name="set">Set onde serão adicionadas as entidades</param>
        /// <param name="identifierExpression">Campos usados na comparação</param>
        /// <param name="entities">Entidades para adicionar</param>
        public static void AddIfNotExists<TEntity>(this IDbSet<TEntity> set, Expression<Func<TEntity, object>> identifierExpression, params TEntity[] entities) where TEntity : class
        {

            var identifyingProperties = GetProperties<TEntity>(identifierExpression).ToList();
            var parameter = Expression.Parameter(typeof(TEntity));
            foreach (var entity in entities)
            {
                var matches = identifyingProperties.Select(pi => Expression.Equal(Expression.Property(parameter, pi.Name), Expression.Constant(pi.GetValue(entity, null))));
                var matchExpression = matches.Aggregate<BinaryExpression, Expression>(null, (agg, v) => (agg == null) ? v : Expression.AndAlso(agg, v));

                var predicate = Expression.Lambda<Func<TEntity, bool>>(matchExpression, new[] { parameter });
                if (!set.Any(predicate))
                {
                    set.Add(entity);
                }
            }
        }

        private static IEnumerable<PropertyInfo> GetProperties<T>(Expression<Func<T, object>> exp) where T : class
        {
            Debug.Assert(exp != null);
            Debug.Assert(exp.Body != null);
            Debug.Assert(exp.Parameters.Count == 1);

            var type = typeof(T);
            var properties = new List<PropertyInfo>();

            if (exp.Body.NodeType == ExpressionType.MemberAccess)
            {
                var memExp = exp.Body as MemberExpression;
                if (memExp != null && memExp.Member != null)
                    properties.Add(type.GetProperty(memExp.Member.Name));
            }
            else if (exp.Body.NodeType == ExpressionType.Convert)
            {
                var unaryExp = exp.Body as UnaryExpression;
                if (unaryExp != null)
                {
                    var propExp = unaryExp.Operand as MemberExpression;
                    if (propExp != null && propExp.Member != null)
                        properties.Add(type.GetProperty(propExp.Member.Name));
                }
            }
            else if (exp.Body.NodeType == ExpressionType.New)
            {
                var newExp = exp.Body as NewExpression;
                if (newExp != null)
                    properties.AddRange(newExp.Members.Select(x => type.GetProperty(x.Name)));
            }

            return properties.OfType<PropertyInfo>();
        }

        /// <summary>
        /// Faz um set.Any(predicate)
        /// Se não existe nada no set então adiciona
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="set">Set onde será adicionada a entidade</param>
        /// <param name="predicate">Condição (exemplo: dbUser => dbUser.Nome == "Gustavo")</param>
        /// <param name="entity">Entidade para adicionar</param>
        /// <returns></returns>
        public static T AddIfNotExists<T>(this IDbSet<T> set, Expression<Func<T, bool>> predicate, T entity) where T : class, new()
        {
            return !set.Any(predicate) ? set.Add(entity) : null;
        }
    }
}

Answer 5

Quoted from MSDN EF article .

Insert or update pattern

A common pattern for some applications is to either Add an entity as new (resulting in a database insert) or Attach an entity as existing and mark it as modified (resulting in a database update) depending on the value of the primary key. For example, when using database generated integer primary keys it is common to treat an entity with a zero key as new and an entity with a non-zero key as existing. This pattern can be achieved by setting the entity state based on a check of the primary key value.

Note that when you change the state to Modified all the properties of the entity will be marked as modified and all the property values will be sent to the database when SaveChanges is called.

context.Entry(profile).State = profile.Id == 0 ? EntityState.Added : EntityState.Modified; 
context.SaveChanges(); 

Answer 6

What worked for me is this:

public static void AddIfNotExists<T>(this DbSet<T> dbSet, Func<T, object> predicate, params T [] entities) where T : class, new()
{
    foreach (var entity in entities)
    {
        var newValues = predicate.Invoke(entity);
        Expression<Func<T, bool>> compare = arg => predicate(arg).Equals(newValues);
        var compiled = compare.Compile();
        var existing = dbSet.FirstOrDefault(compiled);
        if (existing == null)
        {
            dbSet.Add(entity);
        }
    }
}

Answer 7

唯一想到的是使用IEqualityComparer<T> ，但这并没有真正停止工作，只是将其抽象出来并创建更清晰的代码。