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Hello--</div>
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I use postgresql-simple and for selecting rows from one table I have the following function.</div>
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<span style="font-family: Consolas, Courier, monospace; font-size: 10pt;">runMyQuery :: Connection</span></div>
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<span style="font-family: Consolas, Courier, monospace; font-size: 10pt;"> -> String -- query with '?' params to bind</span><br>
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<span style="font-family: Consolas, Courier, monospace; font-size: 10pt;"> -> Int -- first param</span></div>
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<span style="font-family: Consolas, Courier, monospace; font-size: 10pt;"> -> Int -- second param</span></div>
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<span style="font-family: Consolas, Courier, monospace; font-size: 10pt;"> -> IO [MyTable1]</span></div>
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<span style="font-family: Consolas, Courier, monospace; font-size: 10pt;">runMyQuery conn dbQuery param1 param2 = query conn dbQuery $ (param2, param2)</span></div>
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<span style="font-family: Consolas, Courier, monospace; font-size: 10pt;">data MyTable1 = MyTable1 {col1 :: Int, col2 :: Int, col3 :: String}</span></div>
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<span style="font-family: Consolas, Courier, monospace; font-size: 10pt;">instance FromRow MyTable1 where fromRow = MyTable1 <$> field <*> field <*> field <*> field</span></div>
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There are some things I'd like to improve:</div>
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<li class="elementToProof"><span>I will have to write "MyTable1", "MyTable2", ... datatypes, one for each table, but would like to have only one function runMyQuery where the return type is a generic IO [MyModel]. My problem is that I don't know how to write
it for tables with different number of columns and different SQL types.</span></li><li class="elementToProof"><span>The 2nd<span> </span>to the penultimate arguments of runMyQuery are the arguments to bind into the SQL string query. This means that I should write several different version of "runMyQuery" each with a different number of arguments,
but would like to have only one.</span></li></ol>
<div class="elementToProof">Can you recommend some approaches?</div>
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<div class="elementToProof">Thanks.</div>
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