public static Func<TDbTable, bool> GetWhereClauseForAll<TDbTable, TEntity>(
this List<TEntity> objects,
Func<TEntity, Func<TDbTable, bool>> comparison)
{
Func<Func<TDbTable, bool>, Func<TDbTable, bool>, Func<TDbTable, bool>> concatWhereClauses
= (existingWhereClause, toBeAddedWhereClause)
=> row
=> existingWhereClause(row) || toBeAddedWhereClause(row);
Func<TDbTable, bool> whereClause = comparison(objects.First());
for (int i = 1; i < objects.Count; i++)
whereClause = concatWhereClauses(whereClause, comparison(objects[i]));
return whereClause;
}
Refactorings
No refactoring yet !
Ants
November 16, 2009, November 16, 2009 08:57, permalink
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One of these two is more readable and easier to understand depending on how well your brain can parse things. Although, I posted the compact form first, I actually got to the compact form by iteratively simplifying the verbose form.
public static Func<TDbTable, bool> GetWhereClauseForAll<TDbTable, TEntity>(
this List<TEntity> objects,
Func<TEntity, Func<TDbTable, bool>> comparison)
{
return dbTable => objects.Any(entity => comparison(entity)(dbTable));
}
public static Func<TDbTable, bool> GetWhereClauseForAll<TDbTable, TEntity>(
this List<TEntity> objects,
Func<TEntity, Func<TDbTable, bool>> comparison)
{
Func<TDbTable, bool> whereClause =
(TDbTable dbTable) =>
{
foreach (TEntity entity in objects)
{
Func<TDbTable, bool> compare = comparison(entity);
if (compare(dbTable))
return true;
}
return false;
};
return whereClause;
}
Suddenly found myself having written this piece of ugly Extension method, and I'm wondering if there is a more clear way of doing this.
The idea is that given a list of objects, I want to generate the where expression/func that will give me all rows in the database (TDbTable), and I have a comparison that will match TEntity to TDbTable. In reality it generates this kind of SQL: "WHERE id = 1 or id = 2 or id = 3 ... "