Question

我为Microsoft.EntityFrameworkCore构建了一个扩展，该扩展实现了AddOrUpdateMethod。它工作正常，但是对于具有复合主键的实体，AnyAsync方法始终返回false，即使有些对象具有相同的键。

这是方法：

public static async Task AddOrUpdateAsync<TEntity>(this DbSet<TEntity> table, Expression<Func<TEntity, object>> key, Expression<Func<TEntity, bool>> deleteExpression, params TEntity[] entities) where TEntity : class
{
    var getKeyFunction = key.Compile();
    var getShouldDeleteFunction = deleteExpression.Compile();
    var context = GetDbContext(table);
    foreach (var entity in entities)
    {
        var primaryKey = getKeyFunction(entity);
        var body = Expression.Equal(Expression.Convert(key.Body, primaryKey.GetType()), Expression.Constant(primaryKey));
        Expression<Func<TEntity, bool>> query = Expression.Lambda<Func<TEntity, bool>>(body, key.Parameters);
        var exist = await table.AnyAsync(query);
        context.Entry(entity).State = exist
            ? getShouldDeleteFunction(entity) ? EntityState.Deleted : EntityState.Modified
            : getShouldDeleteFunction(entity) ? EntityState.Detached : EntityState.Added;
    }
}

private static DbContext GetDbContext<T>(this DbSet<T> table) where T : class
{
    var infrastructure = table as IInfrastructure<IServiceProvider>;
    var serviceProvider = infrastructure.Instance;
    var currentDbContext = serviceProvider.GetService(typeof(ICurrentDbContext)) as ICurrentDbContext;
    return currentDbContext.Context;
}

我正在这样使用它：

await db.Reports.AddOrUpdateAsync(r => new { r.Number, r.Year }, r => r.Active == false, response.Reports.ToArray());

我认为这是因为我使用匿名类型作为密钥，但是我不知道如何解决这个问题。

Answer 1

问题似乎出在使用匿名类型常量表达式，该表达式当前导致client evaluation，C＃运算符==通过引用比较匿名类型，因此总是返回false。

获得所需服务器翻译的技巧是通过用key替换参数来用entity“调用” Expression.Constant(entity)表达式（Expression.Invoke在这种情况）

因此，不再需要行var getKeyFunction = key.Compile();，并使用以下命令：

foreach (var entity in entities)
{
    var parameter = key.Parameters[0];
    var body = Expression.Equal(
        key.Body,
        key.Body.ReplaceParameter(parameter, Expression.Constant(entity))
    );
    var query = Expression.Lambda<Func<TEntity, bool>>(body, parameter);
    var exist = await table.AnyAsync(query);
    // ...
}

其中ReplaceParameter是常用的表达式帮助器方法：

public static partial class ExpressionUtils
{
    public static Expression ReplaceParameter(this Expression expression, ParameterExpression source, Expression target)
        => new ParameterReplacer { Source = source, Target = target }.Visit(expression);

    class ParameterReplacer : ExpressionVisitor
    {
        public ParameterExpression Source;
        public Expression Target;
        protected override Expression VisitParameter(ParameterExpression node)
            => node == Source ? Target : node;
    }
}

具有复合键的自定义EF Core AddOrUpdate

1 个答案: