在Include语句中使用Where子句的Linq查询

本文关键字：子句 Linq 查询 Where Include 语句 | 更新日期: 2023-09-27 18:20:30

我正在尝试替换我的又大又丑的查询；虽然丑陋，但它工作如所愿：-

using (var ctx = new Data.Model.xxxTrackingEntities())
{
    var result = ctx.Offenders
        .Join(ctx.Fees, o => o.OffenderId, f => f.OffenderId,
        (o, f) => new { Offenders = o, Fees = f })
        .Join(ctx.ViolationOffenders, o => o.Fees.ViolationId, vo => vo.ViolationId,
        (o, vo) => new { Offenders = o, ViolationOffenders = vo })
        .Join(ctx.Violations, v => v.ViolationOffenders.ViolationId, vo => vo.ViolationId,
        (v, vo) => new { Violations = v, ViolationOffenders = vo })
        .Where(o => o.Violations.Offenders.Offenders.YouthNumber != "")
        .ToList();
    gvwData.DataSource = result;
}

使用以下linq查询：-

 var result = ctx.Offenders
        .Include(o => o.Fees.Where(f => f.Amount != null))
        .Include(o => o.ViolationOffenders)
        .Include(o => o.ViolationOffenders.Select(of => of.Violation))
        .Where(o => o.YouthNumber != "" && o.FirstName != "")
        .ToList();

我在查询的第二行爆炸了。。。一旦我加上Where子句。。。o => o.Fees.Where(f=> f.Amount != null)

我收到的错误消息。。。

Include路径表达式必须引用在类型上定义的导航属性。对引用导航属性使用虚线路径，对集合导航属性使用Select操作符。

此外，我尝试将我的查询写成：-

   var result = ctx.Offenders
        .Include(o => o.Fees)
        .Include(o => o.ViolationOffenders)
        .Include(o => o.ViolationOffenders.Select(of => of.Violation))
        .Where(o => o.YouthNumber != "" && o.FirstName != "" && o.Fees.Where(f=> f.Amount != null))
        .ToList();

但后来我得到了以下错误：-

操作员的&amp；'不能应用于类型为"bool"answers"System.Collections.Generic.IEnumerable "的操作数

我知道这个概念是正确的，但我需要语法方面的帮助。

在Include语句中使用Where子句的Linq查询

Where中不能有Where，但可以使用Any，它将返回布尔

var result = ctx.Offenders
    .Include(o => o.Fees)
    .Include(o => o.ViolationOffenders)
    .Include(o => o.ViolationOffenders.Select(of => of.Violation))
    .Where(o => o.YouthNumber != "" && o.FirstName != "" 
        && o.Fees.Any(f=> f.Amount != null)) // here
    .ToList();

在.Net 5中添加了过滤包含功能（EF Core 5.0）。

支持的操作有：Where、OrderBy、OrderByDescending、ThenBy、ThenByDescening、Skip和Take

using (var context = new BloggingContext())
{
    var filteredBlogs = context.Blogs
        .Include(blog => blog.Posts
            .Where(post => post.BlogId == 1)
            .OrderByDescending(post => post.Title)
            .Take(5))
        .ToList();
}

MSDN参考：https://learn.microsoft.com/en-us/ef/core/querying/related-data/eager

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