c# - 模拟 DbContext SaveChanges() 方法不返回任何值

Question

我想知道是否有人知道在使用 Moq 模拟 DbContext 时导致 SaveChanges() 返回 0 以外的值的方法。我经常在我的代码中使用 SaveChanges() 来在已保存或未保存的项目更改数量小于或大于预期的更改数量时抛出错误。

根据我使用 Moq 的经验，如果您不调用数据库，DbContext.SaveChanges() 似乎不会做任何事情。

2016 年 9 月 8 日更新

Jeroen Heier 和 Nkosi 的建议帮助提供了解决方案。我应该更深入地研究 Mock 并意识到 SaveChanges() 是一个虚拟的(duh!)。作为引用，我将添加下面的代码来演示我在做什么。需要注意的一件事是，如果您的业务逻辑取决于保存到数据库中的项目数，则需要定义一个回调来保存更改 DbContext.Setup().Callback(() => {/* 做点什么 */})。使用回调，您可以跟踪调用保存更改的预期次数，并在您的测试中断言它们。

PostService 类中的“SavePost”方法

public PostViewModel SavePost(PostViewModel currentPost, bool publishPost)
{
    //_context.Configuration.ProxyCreationEnabled = false;

    JustBlogContext currentContext = (JustBlogContext)_Context;
    Post newPost = new Post();
    List<Tag> postTags = new List<Tag>();
    DateTime currentDateTime = DateTime.UtcNow;
    bool saveSuccess = false;

    if (currentPost != null)
    {
        //Post
        newPost = new Post()
        {
            Category = currentPost.Category.Id.Value,
            Description = currentPost.Description,
            ShortDescription = currentPost.ShortDescription,
            Title = currentPost.Title,
            UrlSlug = currentPost.UrlSlug,
            Published = currentPost.Published == true || publishPost == true ? true : false,
            Meta = currentPost.Meta == "" || currentPost.Meta == null ? "No meta data" : currentPost.Meta,
            PostedOn = currentPost.PostedOn,
            Modified = currentDateTime
        };

        //Tags
        foreach (Tag currentTag in currentPost?.Tags)
        {
            postTags.Add(new Tag()
            {
                Description = currentTag.Description,
                Id = currentTag.Id,
                Name = currentTag.Name,
                UrlSlug = currentTag.UrlSlug
            });
        }

        if (currentPost.PostedOn == null && publishPost)
        {
            newPost.PostedOn = currentDateTime;
        }

        /**
         * Note that you must track all entities
         * from the Post side of the Post - PostTagMap - Tag database schema.
         * If you incorrectly track entites you will add new tags as opposed to
         * maintaining the many-to-many relationship.
         **/
        if (currentPost?.Id == null)
        {
            //Add a new post
            //Attach tags from the database to post
            foreach (Tag clientTag in postTags)
            {
                if (currentContext.Entry(clientTag).State == EntityState.Detached)
                {
                    currentContext.Tags.Attach(clientTag);
                }
            }

            newPost.Tags = postTags;
            currentContext.Posts.Add(newPost);
            saveSuccess = currentContext.SaveChanges() > 0 ? true : false;
        }
        else
        {
            //Modify and existing post.
            bool tagsModified = false;
            newPost.Id = currentPost.Id.Value;
            currentContext.Posts.Attach(newPost);
            currentContext.Entry(newPost).State = EntityState.Modified;

            saveSuccess = currentContext.SaveChanges() > 0 ? true : false;
            List<Tag> dataTags = currentContext.Posts.Include(post => post.Tags).FirstOrDefault(p => p.Id == newPost.Id).Tags.ToList();

            //Remove old tags
            foreach (Tag tag in dataTags)
            {
                if (!postTags.Select(p => p.Id).ToList().Contains(tag.Id))
                {
                    tagsModified = true;
                    newPost.Tags.Remove(tag);
                }
            }

            if (postTags.Count() > 0)
            {
                //Add new tags
                foreach (Tag clientTag in postTags)
                {
                    //Attach each tag because it comes from the client, not the database
                    if (!dataTags.Select(p => p.Id).ToList().Contains(clientTag.Id))
                    {
                        currentContext.Tags.Attach(clientTag);
                    }

                    if (!dataTags.Select(p => p.Id).ToList().Contains(clientTag.Id))
                    {
                        tagsModified = true;
                        newPost.Tags.Add(currentContext.Tags.Find(clientTag.Id));
                    }
                }

                //Only save changes if we modified the tags
                if (tagsModified)
                {
                    saveSuccess = currentContext.SaveChanges() > 0 ? true : false;
                }
            }
        }
    }

    if (saveSuccess != false)
    {
        return loadEditedPost(currentContext, newPost);
    }
    else
    {
        throw new JustBlogException($"Error saving changes to {newPost.Title}");
    }
}

PostService_Test.cs 中的“SavePost_New_Post_Test”测试方法

/// <summary>
/// Test saving a new post
/// </summary>
[TestMethod]
public void SavePost_New_Post_Test()
{
    //Arrange
    var postSet_Mock = new Mock<DbSet<Post>>();

    var justBlogContext_Mock = new Mock<JustBlogContext>();
    justBlogContext_Mock.Setup(m => m.Posts).Returns(postSet_Mock.Object);

    IPostService postService = new PostService(justBlogContext_Mock.Object);

    // setup Test
    CategoryViewModel newCategory = new CategoryViewModel()
    {
        Description = "Category Description",
        Id = 0,
        Modified = new DateTime(),
        Name = "Name",
        PostCount = 0,
        Posts = new List<Post>(),
        UrlSlug = "Category Url Slug"
    };

    Tag newTag = new Tag()
    {
        Description = "Tag Description",
        Id = 1,
        Modified = new DateTime(),
        Name = "Tag Name",
        Posts = new List<Post>(),
        UrlSlug = "Url Slug"
    };

    Tag newTag2 = new Tag()
    {
        Description = "Tag Description 2",
        Id = 2,
        Modified = new DateTime(),
        Name = "Tag Name 2",
        Posts = new List<Post>(),
        UrlSlug = "UrlSlug2"
    };

    List<Tag> tags = new List<Tag>();

    tags.Add(newTag);
    tags.Add(newTag2);

    // setup new post
    PostViewModel newPost = new PostViewModel()
    {
        Category = newCategory,
        Description = "Test Descritpion",
        Meta = "Meta text",
        Modified = new DateTime(),
        Published = false,
        PostedOn = null,
        ShortDescription = "Short Description",
        Title = "TestTitle",
        UrlSlug = "TestUrlSlug",
        Tags = tags,
        Id = null
    };

    // counters to verify call order
    int addPostCount = 0;
    int addTagAttachCount = 0;
    int saveChangesCount = 0;
    int totalActionCount = 0;

    // Register callbacks to keep track of actions that have occured
    justBlogContext_Mock.Setup(x => x.Posts.Add(It.IsAny<Post>())).Callback(() =>
    {
        addPostCount++;
        totalActionCount++;
    });

    justBlogContext_Mock.Setup(x => x.SaveChanges()).Callback(() =>
    {
        saveChangesCount++;
        totalActionCount++;
    });

    justBlogContext_Mock.Setup(x => x.SaveChanges()).Returns(1);

    justBlogContext_Mock.Setup(x => x.Tags.Attach(It.IsAny<Tag>())).Callback(() =>
    {
        addTagAttachCount++;
        totalActionCount++;
    });          

    // Act
    postService.SavePost(newPost, false);
    // Assert
    justBlogContext_Mock.Verify(m => m.SaveChanges(), Times.AtLeastOnce());
    Assert.IsTrue(addPostCount == 1);
    Assert.IsTrue(addTagAttachCount == 2);
    Assert.IsTrue(totalActionCount == 4);
}

Answer 1

假设一个接口(interface)/抽象像

public interface IDbContext {
    int SaveChanges();
}

您可以像这样设置模拟。

var expected = 3;
var mock = new Mock<IDbContext>();
mock.Setup(m => m.SaveChanges()).Returns(expected);


var context = mock.Object;

var actual = context.SaveChanges();

Assert.AreEqual(expected, actual);