Question

在EF6中，我从数据库加载我的机场：

var existingAirport = db.Airports.SingleOrDefault(a => a.ID == airportID)
//airport is loaded, it has a countryID and virtual Country object

我执行一些逻辑，进行一些修改以改变关系，改变国家对象和FK ID：

//it's a bit more complex, but simplified:
existingAirport.Country = //the someOtherCountryObject
existingAirport.CountyID = //the someOtherCountryObject.ID

我保存更改（应该将机场分配给新国家/地区）

db.SaveChanges();

问题是EF决定使DB和内存中的关系为空（existingAirport.Country和existingAirport.CountyID现在都为null）。机场现在与新旧国家相关联。

有人能想到EF这样做的原因吗？新的FK指向一个有效的国家。

Answer 1

看起来您正在尝试添加新的国家/地区，但我没有看到您的新国家/地区实体已添加到上下文中。

请参阅这些帖子以获得一个想法。 Updating child objects in Entity Framework 6和Entity Framework 6: Adding child object to parent's list vs. setting child's navigation property to parent

Answer 2

我花了一段时间，但这是由我模型其他部分的循环引用引起的。例如，我持有一个国家/地区列表，其中一个国家/地区对象（在这种情况下为 someOtherCountryObject ）具有EF生成的对机场的引用。

我通过在映射阶段忽略这些引用来解决问题，即在将国家/地区映射到数据库时：

tinymce.init({
            selector: '#title, #thumbnail_title',
            height: 100,
            theme: 'modern',
            menubar: 'edit insert format tools',

            plugins: 'searchreplace autolink directionality image link media advlist textcolor wordcount imagetools contextmenu colorpicker textpattern code',
            toolbar1: 'formatselect fontselect fontsizeselect | bold italic strikethrough forecolor backcolor | alignleft aligncenter alignright alignjustify  | numlist bullist outdent indent  | removeformat code',
            image_advtab: true,
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            image_class_list: [
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                '//fonts.googleapis.com/css?family=Amaranth|Anton|Dancing+Script|Didact+Gothic|Fira+Sans+Condensed|Francois+One|Lato|Lobster|Lobster+Two|Muli|Open+Sans|Pacifico|Passion+One|Playfair+Display|Playfair+Display+SC|Quattrocento|Quattrocento+Sans|Sanchez|Shadows+Into+Light|Shadows+Into+Light+Two|Spectral+SC|Yrsa',

            ],
            font_formats : 'Andale Mono=andale mono,times;Arial=arial,helvetica,sans-serif;Arial Black=arial black,avant garde;Book Antiqua=book antiqua,palatino;Comic Sans MS=comic sans ms,sans-serif;Courier New=courier new,courier;Georgia=georgia,palatino;Helvetica=helvetica;Impact=impact,chicago;Symbol=symbol;Tahoma=tahoma,arial,helvetica,sans-serif;Terminal=terminal,monaco;Times New Roman=times new roman,times;Trebuchet MS=trebuchet ms,geneva;Verdana=verdana,geneva;Webdings=webdings;Wingdings=wingdings,zapf dingbats;Didact Gothic=Didact Gothic, sans-serif;Open Sans=Open Sans, sans-serif;Lato=Lato, sans-serif;Spectral SC=Spectral SC, serif;Playfair Display SC=Playfair Display SC, serif;Muli=Muli, sans-serif;Anton=Anton, sans-serif;Lobster=Lobster, cursive;Lobster Two=Lobster Two, cursive;Playfair Display=Playfair Display, serif;Pacifico=Pacifico, cursive;Shadows Into Light=Shadows Into Light, cursive;Shadows Into Light Two=Shadows Into Light Two, cursive;Dancing Script=Dancing Script, cursive;Francois One=Francois One, sans-serif;Passion One=Passion One, cursive;Sanchez=Sanchez, serif;Quattrocento Sans=Quattrocento Sans, sans-serif;Quattrocento=Quattrocento, serif;Amaranth=Amaranth, sans-serif;Fira Sans Condensed=Fira Sans Condensed, sans-serif;Yrsa=Yrsa, serif;',

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            verify_html: true,
            branding:false,
            theme_advanced_fonts : ''
        });

这解决了这个问题，防止EF在调用SaveChanges（）时使关系无效。我的Aiport现在拥有应该拥有的国家，并且没有发生重复或任何副作用。

保存时，EntityFramework使FK关系为空

2 个答案: