Lambda表达式到SQL UPDATE语句使用C＃ [英] Lambda expression to SQL UPDATE statement using C#

问题描述

库或代码是否可用于从lambda表达式创建SQL Update语句？我们希望使用强类型的lambda表达式来进行更新，而不是在手之前或使用字符串调用对象。我正在想这样的事情。

Is library or code available to create SQL Update statements from lambda expressions? We would like to use strongly-typed lambda expressions to do updates instead of calling the object before hand, or using strings. I'm thinking of something like this.

Update<Task>(
    u => u.UserID = 1, u.TaskCount += 1, //Update
    w => w.Priority != "High" && (w.Status != "Complete" || w.Status == null) //Where
);

哪些将大致转换为..

Which would roughly translate to..

UPDATE Tasks SET UserID = 1, TaskCount = TaskCount + 1
WHERE Priority <> "High" AND (Status <> "Complete" OR Status = null)

我应该提到我们正在使用实体框架和Postgres。

I should mention we are currently using the Entity Framework and Postgres.

推荐答案

我终于想出了一个办法。基本上，从实体框架，LINQ到SQL或其他ORM获取生成的SQL，然后解析WHERE子句。这样我就不必手动解析lambda了。然后从匿名类型创建UPDATE子句。结果如下：

I finally figured out a way to do this. Basically, get the generated SQL from the Entity Framework, LINQ-to-SQL, or another ORM, then parse the WHERE clause. That way I don't have to parse the lambda manually. Then create an UPDATE clause from an anonymous type. The result looks like:

Update<Task>(
    new { UserID = 1, TaskCount = IncrementOf(1), SomeOtherField = DdNull } //Update
    w => w.Priority != "High" && (w.Status != "Complete" || w.Status == null) //Where
);

Delete<Task>(w => w.UserID == userID && w.Status != "Complete");

这允许我更新/删除值，不要先拖动它们。

This allows me to update/delete values WITHOUT pulling them first.

它的代码看起来像这样...

And the code for it looks like this...

protected void Update<T>(object values, Expression<Func<T, bool>> where) where T : class
{
    Domain.ExecuteStoreCommand(
        "UPDATE {0} SET {1} WHERE {2};",
        GetTableString<T>(),
        GetUpdateClauseString(values),
        GetWhereClauseString(where)
        );
}

protected string GetUpdateClauseString(object obj)
{
    string update = "";
    var items = obj.ToDictionary();
    foreach (var item in items)
    {
        //Null
        if (item.Value is DBNull) update += string.Format("{0} = NULL", GetFieldString(item.Key));

        //Increment
        else if (item.Value is IncrementExpression) update += string.Format("{0} = {0} + {1}", GetFieldString(item.Key), ((IncrementExpression)item.Value).Value.ToString());

        //Decrement
        else if (item.Value is DecrementExpression) update += string.Format("{0} = {0} - {1}", GetFieldString(item.Key), ((DecrementExpression)item.Value).Value.ToString());

        //Set value
        else update += string.Format("{0} = {1}", GetFieldString(item.Key), GetValueString(item.Value));

        if (item.Key != items.Last().Key) update += ", ";
    }
    return update;
}

protected string GetWhereClauseString<T>(Expression<Func<T, bool>> where) where T : class
{
    //Get query
    var query = ((IQueryable<T>)Domain.CreateObjectSet<T>());
    query = query.Where(where);
    ObjectQuery queryObj = (ObjectQuery)query;

    //Parse where clause
    string queryStr = queryObj.ToTraceString();
    string whereStr = queryStr.Remove(0, queryStr.IndexOf("WHERE") + 5);

    //Replace params
    foreach (ObjectParameter param in queryObj.Parameters)
    {
        whereStr = whereStr.Replace(":" + param.Name, GetValueString(param.Value));
    }

    //Replace schema name
    return whereStr.Replace("\"Extent1\"", "\"Primary\"");
}

这篇关于Lambda表达式到SQL UPDATE语句使用C＃的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！