林克之间的表现

Question

我正在使用Entity Framework,我想知道以下代码之间是否有任何区别.第一个和第二个代码似乎通过Entidad.Nombre =="Empresa"过滤掉所有项目,最后一个代码似乎只获得Entidad.Nombre =="Empresa"的项目.我错了吗？什么是更好的？

var listFields = from b in unitOfWork.PropiedadRepository.Get()
                         where b.Entidad.Nombre == "Empresa"
                         select b;
var listFields2 = unitOfWork.PropiedadRepository.Get().Where(x => x.Entidad.Nombre == "Empresa");
var listFields3 = unitOfWork.PropiedadRepository.Get(x => x.Entidad.Nombre == "Empresa");

这是GenericRepository类.所有存储库都继承了它.

public sealed class GenericRepository<TEntity> where TEntity : class
{
    private readonly ConfigurationDbDataContext _context;
    private readonly DbSet<TEntity> _dbSet;

    public GenericRepository(ConfigurationDbDataContext context)
    {
        _context = context;
        _dbSet = context.Set<TEntity>();
    }

    public IEnumerable<TEntity> Get(
        Expression<Func<TEntity, bool>> filter = null,
        Func<IQueryable<TEntity>, IOrderedQueryable<TEntity>> orderBy = null,
        string includeProperties = "")
    {
        IQueryable<TEntity> query = _dbSet;

        if (filter != null)
        {
            query = query.Where(filter);
        }

        query = includeProperties.Split(new[] {','}, StringSplitOptions.RemoveEmptyEntries).Aggregate(query, (current, includeProperty) => current.Include(includeProperty));

        // ReSharper disable once ConvertIfStatementToReturnStatement
        if (orderBy != null)
        {
            return orderBy(query).ToList();
        }
        else
        {
            return query.ToList();
        }
    }

    public TEntity GetById(object id)
    {
        return _dbSet.Find(id);
    }

    public void Insert(TEntity entity)
    {
        _dbSet.Add(entity);
    }

    public void Delete(object id)
    {
        var entityToDelete = _dbSet.Find(id);
        Delete(entityToDelete);
    }

    public void Delete(TEntity entityToDelete)
    {
        if (_context.Entry(entityToDelete).State == EntityState.Detached)
        {
            _dbSet.Attach(entityToDelete);
        }
        _dbSet.Remove(entityToDelete);
    }

    public void Update(TEntity entityToUpdate)
    {
        _dbSet.Attach(entityToUpdate);
        _context.Entry(entityToUpdate).State = EntityState.Modified;
    }
}

Answer 1

你是对的.

在最后一种情况下,where子句的评估被赋予dataserver(linq to entities),客户端只接收过滤后的数据.

在其他情况下,客户端接收所有数据,然后过滤它(linq到对象).

那说:我们在谈论什么表现？CPU,网络,客户端,服务器端？

通常,人们更喜欢让服务器过滤器对实体进行过滤,但它实际上取决于某些参数和目标.

请注意linq与实体和linq to object之间最令人惊讶的区别:linq to object是区分大小写的.对于linq到实体,它依赖于数据库/表/列排序规则.

此外,正如Kaspars所提醒的,尾随空格的处理是不同的.