忽略 where 子句中的 null 参数 linq to sql

Question

我需要忽略 where 子句中的空参数，以便我可以使用应用的过滤器从用户端获取适当的数据。为了实现这一点，我目前正在使用 if..else 嵌套方法，它的大小随着参数数量的增加而增加。我想知道是否还有其他有效的方法可以通过避免行数和复杂性并提高可读性来处理这种情况

public List<Members> GetMembers(int currentPosition, string memberStatus,
                string package, string packageStatus, string branch)
{
    var members = new List<Members>();
    if (package != null)
    {
        //include package
        if (packageStatus != null)
        {
            //include package, packageStatus
            if (branch != null)
            {
                //include package,packageStatus,branch
                members = db.Members.Where(x => x.PackageName == package && x.PackageStatus == packageStatus && x.Branch == branch).ToList();
            }
            else
            {
                //include package,packageStatus
                members = db.Members.Where(x => x.PackageName == package && x.PackageStatus == packageStatus).ToList();
            }
        }
        else
        {
            if (branch != null)
            {
                //include package,branch
                members = db.Members.Where(x => x.PackageName == package && x.Branch == branch).ToList();
            }
            else
            {
                //include package
                members = db.Members.Where(x => x.PackageName == package).ToList();
            }
        }
    }
    else
    {
        if (packageStatus != null)
        {
            //include packageStatus
            if (branch != null)
            {
                //include packageStatus,branch
                members = db.Members.Where(x => x.PackageStatus == packageStatus && x.Branch == branch).ToList();
            }
            else
            {
                //include packageStatus
                members = db.Members.Where(x => x.PackageStatus == packageStatus).ToList();
            }
        }
        else
        {
            if (branch != null)
            {
                //include packageStatus,branch
                members = db.Members.Where(x => x.PackageStatus == packageStatus && x.Branch == branch).ToList();
            }
            else
            {
                //include nothing
                members = db.Members.ToList();
            }
        }
    }

    return members;
}

Answer 1

您可以将这些条件添加到查询中。它不会带来最可读的 SQL，但假设您发现可读代码更重要并且信任 SQL 服务器的优化器：

members = db.Members.Where(x =>
    (package == null || x.PackageName == package) &&
    (packageStatus == null || x.PackageStatus == packageStatus) &&
    (branch == null || x.Branch == branch)
).ToList();

或者，您可以有条件地将 Where() 附加到 IQueryable<Member> 类型的变量。例如参见 [=13=].

Answer 2

我想推荐一个可读版本的方法：

public List<Members> GetMembers(int currentPosition, string memberStatus,
    string package, string packageStatus, string branch)
{
    var members = new List<Members>();

    members = db.Members.ToList();

    if (package != null)
    {
        members = members.Where(x => x.PackageName == package);
    }

    if (packageStatus != null)
    {
        members = members.Where(x => x.PackageStatus == packageStatus);
    }

    if (branch != null)
    {
        members = members.Where(x => x.Branch == branch);
    }

    return members.ToList();
}

Answer 3

我认为这可行（还没有尝试编译它，但它在我的脑海中很有意义）

    public List<Members> GetMembers(int currentPosition, string memberStatus,
                string package, string packageStatus, string branch)
    {
        List<Members> ret = db.Members()
        if(memberStatus != null || package != null || packageStatus != null || branch != null)
        {
            ret = db.Members.Where(x => 
                (memberStatus == null) ? (true) : (memberStatus == x.MemberStatus)
                && (package == null) ? (true) : (package == x.PackageName)
                && (packageStatus == null) ? (true) : (packageStatus == x.PackageStatus)
                && (branch == null) ? (true) : (branch == x.Branch)
            ).ToList();
        }
        return ret;
    }

忽略 where 子句中的 null 参数 linq to sql

Ignoring null parameter in where clause linq to sql

c#

maintainability

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