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POHow to specify .NET Anonymous object return type in Linq using Func<T,Q>?
 

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  1. POHow to specify .NET Anonymous object return type in Linq using Func<T,Q>?
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    <p>How do you specify the <strong>Func</strong> signature for anonymous objects?</p> <pre><code>new Func&lt;DataSet, **IEnumerable&lt;int&gt;&gt;** </code></pre> <p>I am having a trouble with return type where I have specified as <strong>IEnumerable&lt;></strong> in the Func declaration</p> <p>Error I am getting from the expression is </p> <blockquote> <p>Cannot convert expression type 'System.Collections.Generic.IEnumerable&lt;{ParentNodeId:int}>' to returnt ype 'System.Collections.Generic.IEnumerable'</p> </blockquote> <p>How can I specify <strong>IEnumerable&lt;{ParentNodeId:int}></strong> in func?</p> <pre><code> public int GetCachedRootNodeId(IList&lt;int&gt; fromNodeIds, int forNodeId) { var result = forNodeId; const string spName = "spFetchAllParentNodeIDs"; using (var ds = _df.ExecuteDatasetParamArray(_ConnectionString, spName, forNodeId)) { if (DataAccessUtil.DataSetIsEmpty(ds)) return result; var orderByLevelDesc = new Func&lt;DataSet, IEnumerable&lt;int&gt;&gt;(resultSet =&gt; from DataRow row in DataAccessUtil.GetFirstTableRows(resultSet) orderby DataAccessUtil.GetInt32(row, "Level") descending select new { ParentNodeId = DataAccessUtil.GetInt32(row, "ParentNodeID") }); //// Get top-most parent's node ID first (higher the level, the more top-most the parent is) //var query = from DataRow row in DataAccessUtil.GetFirstTableRows(ds) // orderby DataAccessUtil.GetInt32(row, "Level") descending // select new { ParentNodeId = DataAccessUtil.GetInt32(row, "ParentNodeID") }; //foreach (var nodeInfo in query) foreach (var nodeInfo in orderByLevelDesc(ds)) { if (fromNodeIds.Contains(nodeInfo.ParentNodeId)) return nodeInfo.ParentNodeId; } } return result; } </code></pre> <p>By the way, I could have used commented code "query" and be done with it. But wanted to be more expressive and try something new after looking at this answer <a href="https://stackoverflow.com/questions/576374/why-doesnt-c-have-lexically-nested-functions/576386#576386">Why doesn't C# have lexically nested functions?</a></p> <p><strong>EDIT</strong>: Final Result</p> <pre><code> public int GetCachedRootNodeId(IList&lt;int&gt; fromNodeIds, int forNodeId) { var result = forNodeId; const string spName = "spFetchAllParentNodeIDs"; using (var ds = _df.ExecuteDatasetParamArray(_ConnectionString, spName, forNodeId)) { if (DataAccessUtil.DataSetIsEmpty(ds)) return result; var orderParentNodeIDByLevelDesc = new Func&lt;DataSet, IEnumerable&lt;int&gt;&gt;(resultSet =&gt; from DataRow row in DataAccessUtil.GetFirstTableRows(resultSet) orderby DataAccessUtil.GetInt32(row, "Level") descending select DataAccessUtil.GetInt32(row, "ParentNodeID")); foreach (var parentNodeId in orderParentNodeIDByLevelDesc(ds)) { if (fromNodeIds.Contains(parentNodeId)) return parentNodeId; } } return result; } </code></pre>
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