EF Core 7报错：LINQ表达式ProjectionBindingExpression无法转换问题求助

问题背景 #

从.NET 5迁移至.NET 7后，原有LINQ查询出现翻译失败错误：EF Core 7 - The LINQ expression 'ProjectionBindingExpression: 14' could not be translated，该查询在EF Core 5/6中可正常执行。

问题代码 #

var query = 
    (from member in organization.Users
    let donor = member.Donor
    select new MembershipVM
    {
        UniqueIdentifier = member.UniqueIdentifier,
        Email = member.Email,

        LastDonation = (from donation in donor.Donations
                        where donation.Fund.OrgId == organization.Id
                        orderby donation.timeCreated descending
                        select new MembershipVM.LastDonationVM
                        {
                            Amount = donation.Amount
                        }).FirstOrDefault()
    })

修复方案 #

方案1：移除中间let绑定，直接使用导航属性 #

EF Core 7对let关键字的嵌套投影翻译存在bug，移除let donor = member.Donor，直接通过member.Donor.Donations访问关联数据，可规避翻译问题：

var query = 
    from member in organization.Users
    select new MembershipVM
    {
        UniqueIdentifier = member.UniqueIdentifier,
        Email = member.Email,
        LastDonation = (from donation in member.Donor.Donations
                        where donation.Fund.OrgId == organization.Id
                        orderby donation.timeCreated descending
                        select new MembershipVM.LastDonationVM
                        {
                            Amount = donation.Amount
                        }).FirstOrDefault()
    };

方案2：改用方法链语法重构查询 #

方法链语法的结构更利于EF Core的翻译器解析，重构后的代码如下：

var query = organization.Users
    .Select(member => new MembershipVM
    {
        UniqueIdentifier = member.UniqueIdentifier,
        Email = member.Email,
        LastDonation = member.Donor.Donations
            .Where(donation => donation.Fund.OrgId == organization.Id)
            .OrderByDescending(donation => donation.timeCreated)
            .Select(donation => new MembershipVM.LastDonationVM { Amount = donation.Amount })
            .FirstOrDefault()
    });

方案3：临时启用客户端评估（不推荐） #

若上述方案无法生效，可临时允许客户端评估（注意：会导致部分查询逻辑在内存中执行，可能影响性能），在DbContext配置中添加：

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
    optionsBuilder
        .UseSqlServer("你的数据库连接字符串")
        .ConfigureWarnings(warnings => warnings.Ignore(CoreEventId.ClientEvaluationWarning));
}

说明 #

该问题是EF Core 7版本特有的查询翻译bug，后续官方更新可能修复此问题，优先推荐使用方案1或2调整查询结构来规避。

内容的提问来源于stack exchange，提问作者Isaac Ikusika