如何在EF Repository Pattern中为GetAllByExpression传入Include表达式参数

解决方法 #

你只需要把需要Include的导航属性表达式，放到对应类型的表达式数组里传入即可，修改你的调用代码如下：

public async Task<IEnumerable<PropertyChargesRate>> GetPropertyChargeRates(int buildingId)
{
    try
    {
        var g = new GenericRepository<PropertyChargesRate>(context);
        var result = await g.GetAllByExpression<PropertyChargesRate>(
            x => x.BuildingId == buildingId, 
            // 传入includes参数：导航属性表达式数组
            new Expression<Func<PropertyChargesRate, object>>[] 
            { 
                x => x.PropertyChargeType 
            });
        return result;
    }
    catch (Exception ex)
    {
        return null;
    }
}

如果需要同时加载多个导航属性，直接在数组里追加表达式即可，示例：

new Expression<Func<PropertyChargesRate, object>>[] 
{ 
    x => x.PropertyChargeType,
    x => x.Building // 第二个要加载的导航属性
}

可选优化建议 #

你的泛型仓储类已经声明了泛型参数<T>，方法GetAllByExpression不需要重复声明泛型参数<T>，修改后的方法定义更简洁，调用时也不需要再指定方法的泛型类型：

// 去掉方法级重复的泛型参数<T>和对应的where约束
public async Task<IEnumerable<T>> GetAllByExpression(Expression<Func<T, bool>> expression,
    Expression<Func<T, object>>[] includes)
{
    if (expression != null)
    {
        IQueryable<T> query = context.Set<T>();
        foreach(var include in includes)
        {
            query = query.Include(include);
        }
        var result = await query.Where(expression).ToListAsync();
        return result;
    }
    else
    {
        throw new ArgumentNullException(nameof(expression), "Invalid expression.");
    }
}

优化后调用代码可以简化为：

var result = await g.GetAllByExpression(
    x => x.BuildingId == buildingId, 
    new Expression<Func<PropertyChargesRate, object>>[] { x => x.PropertyChargeType });

内容的提问来源于stack exchange，提问作者Ibanez1408