将SQL Server 2012地理数据类型与ASP.Net一起使用-DataReader.GetFieldType（x）返回null

Question

I've written an ASP.Net 4 Application which has been working perfectly. However, I decided to make use of the new Geography Data Type in Sql Sever 2012. This worked perfectly on my local machine but fails when I upload.

I get there error "DataReader.GetFieldType(9) returned null." when doing a usual "select * FROM Table" query on a table that contains one of these datatypes.

I have searched the various threads regarding adding a reference to the Microsoft.SqlServer.Types.dll into my project and changing Copy Local to true. However I am getting the same error.

I run the database and the web server on two separate servers so I don't think there are any assemblies on the web server unless I upload them with my project.

Am I missing any other assemblies that are needed? or any other settings?

I've taken days trying to solve this and uploading variouse libraries. Any help would be appreciated.

Answer 1

From what I can tell you will at least need SQL Server installed locally when you initially add the reference. If you can I would try and install SQL Express locally first (you do not need to use it just install it) and then try your code again to see if that is the problem.

References:

DataReader.GetFieldType returned null

http://blogs.bing.com/maps/2013/08/05/advance-spatial-queries-using-entity-framework-5/

Edit:

I am more familiar with using spatial types via the entity framework. It seems if you want to use them directly you need to use a nuget package in order to get the required DLLs into the project. From the Microsoft ADO.NET blog page

SqlServerSpatial110.dll – This is a native assembly so it cannot be added as a project reference.

References:

Microsoft ADO.NET Blog

http://blogs.msdn.com/b/adonet/archive/2013/12/09/microsoft-sqlserver-types-nuget-package-spatial-on-azure.aspx

Relevant SO Questions

'Microsoft.SqlServer.Types' version 10 or higher could not be found on Azure https://gis.stackexchange.com/questions/382/how-can-i-use-sql-servers-spatial-types-from-a-net-application

Answer 2

msdn

When the compatibility level is 100 or below in SQL Server 2012 then the geography data type has the following restrictions:

•Each geography instance must fit inside a single hemisphere. No spatial objects larger than a hemisphere can be stored.

•Any geography instance from an Open Geospatial Consortium (OGC) Well-Known Text (WKT) or Well-Known Binary (WKB) representation that produces an object larger than a hemisphere throws an ArgumentException.

•The geography data type methods that require the input of two geography instances, such as STIntersection(), STUnion(), STDifference(), and STSymDifference(), will return null if the results from the methods do not fit inside a single hemisphere. STBuffer() will also return null if the output exceeds a single hemisphere.

Answer 3

Spent heaps of time on this, adding references as well, but I found a workaround i want to share. Should work fine on asp.net as well.

I use the following query to parse me the string representation of the object:

DECLARE @result geography;
SELECT @result = area FROM news WHERE id LIKE @id ;
SELECT ...,  @result.STAsText() as area FROM news WHERE id LIKE @id;

And in the asmx (c#) webservice i retrieved my SQLGeography with a parser method:

row["area"].ToString()

After that you can use a parser method to retrieve the SQLGeography object.

/// <summary>
/// Converts a String into an sql geography object.</summary>
/// <param name="pText">The string representation of the sql geography object. </param>
public static SqlGeography GetGeographyFromText(String pText)
{
    SqlString ss = new SqlString(pText);
    SqlChars sc = new SqlChars(ss);
    try
    {
        if (pText.Contains("POINT"))
        {
            return SqlGeography.STPointFromText(sc, 4326);
        }
        return SqlGeography.STPolyFromText(sc, 4326);
    }
    catch (Exception ex)
    {
        return SqlGeography.STMPolyFromText(sc, 4326);
        throw ex;
    }
}

Hope it helps anyone!

Answer 4

In the end I couldn't get it to work as it does on my development machine and I don't want to install Visual Studio or SQL Server Express on the web server so instead I just removed all the queries where I did "SELECT * FROM Table" and the error went away. It still let me do my calculations using the geography field, but doesn't like you trying to show it on the screen. Thanks for all your help!