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.我也好 :)

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;
}

我现在需要通过另外两个表连接来正确应用过滤器,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中它将是这样的:

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表达式使用的是先前的表达式结果,并且在迭代之前不会实际执行整个表达式.

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");
}