LINQ - 加入动态查询

Question

由于一些商业决策，我需要改变一些我正在做的事情。耶我。 :)

目前，我有：

public IOrderedQueryable<ProductDetail> GetProductList(string productGroupName, string productTypeName, Dictionary<string,List<string>> filterDictionary)
{
    string whereClause = "ProductGroupName='" + productGroupName + "' AND ProductTypeName='" + productTypeName + "'";
    string comma = "";
    foreach (KeyValuePair<string, List<string>> myKVP in filterDictionary)
    {
        comma = "";
        if (myKVP.Value.Count > 0)
        {
            whereClause = String.Format("{0} AND FieldName = {1} AND FieldValue IN (", whereClause, myKVP.Key);
            foreach (string value in myKVP.Value)
            {
                whereClause = String.Format("{0}{1}'{2}'", whereClause, comma, value);
                comma = ",";
            }
            whereClause = String.Format("{0})", whereClause);
        }
    }

    var q = db.ProductDetail
              .Where (whereClause)
              .OrderBy ("ProductTypeName");
    return q;
}

我现在需要通过其他 2 个表加入来正确应用过滤器，而不是直接使用它。我试图弄清楚如何正确加入动态 LINQ 查询。在 TSQL 中会是这样的：

SELECT pd.* 
  FROM ProductDetail pd
 INNER JOIN ProductFilterAssignment pfa ON pd.ProductID = pfs.ProductID
 INNER JOIN ProductFilter pf ON pfs.FIlterID = pf.FIlterID
 WHERE pf.FieldName = 'var1' AND pf.FieldValue IN ('var1a','var1b','var1c',etc)
   AND pf.FieldName = 'var2' AND pf.FieldValue IN ('var2a','var2b','var2c',etc)

Answer 1

哎哟。是的，这是一个复杂的要求。你知道，lambdas 是累积的，所以如果你使用连续的 linq 表达式，你可以更简单地做到这一点。请注意，后续的 linq 表达式正在使用先前的表达式结果，并且整个表达式在迭代之前不会真正执行。

public IOrderedQueryable<ProductDetail> GetProductList(string productGroupName, string productTypeName, Dictionary<string,List<string>> filterDictionary)
{
    // Initial select on productGroupName and productTypeName
    var products = from product in db.ProductDetail
                   where product.ProductGroupName == productGroupName && product.ProductTypeName == productTypeName
                   select product;

    // Now add each filter item present.
    foreach (KeyValuePair<string, List<string>> myKVP in filterDictionary)
    {
        products = from product in products
                   join pfa in db.ProductFilterAssignment on product.ProductID equals pfa.ProductID
                   join pf in db.Product on pfa.FilterID equals pf.FilterId
                   where pf.FieldName == myKVP.Key && myKVP.Value.Contains(pf.FieldValue)
                   select product;
    }

    return products.OrderBy ("ProductTypeName");
}

Answer 2

我没有给你一个好的“答案”，但更多的是一个旁白。查看LINQPad。您甚至可能会在此页面的右侧看到广告。编写 LINQ 查询非常流畅。它可能有助于编写和验证此查询以及您编写的任何其他未来 LINQ 查询。

Answer 3

尝试使用Spolty Framework。它有助于对 Linq To SQL 和实体框架进行动态查询。您可以动态创建左/内连接、添加条件、排序和其他内容。如果您使用 Spolty 框架，那么您的代码将如下所示：

public IQueryable<ProductDetail> GetProductList(string productGroupName, string productTypeName, Dictionary<string, List<string>> filterDictionary)
{
    // create root node 
    JoinNode productDetailNode = new JoinNode(typeof(ProductDetail));
    productDetailNode.AddConditions(new Condition("ProductGroupName", productGroupName),
                    new Condition("ProductTypeName", productTypeName));

    // if there are conditions than we create joins
    if (filterDictionary.Count > 0)
    {
        // create joinNode  
        // INNER JOIN ProductFilterAssignment pfa ON pd.ProductID = pfs.ProductID
        JoinNode productFilterAssignmentNode = new JoinNode(typeof(ProductFilterAssignment));
        productDetailNode.AddChildren(productFilterAssignmentNode);

        // create joinNode  
        // INNER JOIN ProductFilter pf ON pfs.FIlterID = pf.FIlterID
        JoinNode productFilterNode = new JoinNode(typeof(ProductFilter));
        productFilterNode.AddChildren(productFilterNode);

        foreach (KeyValuePair<string, List<string>> myKVP in filterDictionary)
        {
            // create condition pf.FieldName = {1} And AND pf.FieldValue IN ('var1a','var1b','var1c',etc)
            productFilterNode.AddConditions(new Condition("FieldName", myKVP.Key),
                                            OrCondition.Create("FieldValue", myKVP.Value.ToArray()));
        }
    }

    // create result query by JoinNode productDetailNode
    QueryDesigner queryDesigner = new QueryDesigner(db, productDetailNode).
                                        OrderBy(new Ordering("ProductTypeName"));

    return queryDesigner.Cast<ProductDetail>();
}