How to Create Dynamic WHERE Clauses in LINQ for Flexible Data Filtering?

Dynamic LINQ WHERE clause

When using LINQ queries, you may need to dynamically generate WHERE clauses based on user input. This can be achieved by chaining multiple WHERE clauses together, as in the following example:

The

GetProductList() method accepts a dictionary as a parameter, which represents a set of filter conditions. Then, use a where clause to build a LINQ query to filter the results based on the conditions in the dictionary.

Each where clause is added to the query by checking whether the corresponding key exists in the dictionary. If present, filters the query based on the value associated with that key.

The following code example demonstrates how to implement this method:

public IOrderedQueryable<productdetail> GetProductList(string productGroupName, string productTypeName, Dictionary<string, List<string>> filterDictionary)
{
    var q = from c in db.ProductDetail
            where c.ProductGroupName == productGroupName && c.ProductTypeName == productTypeName
            select c; //添加select c;避免编译错误

    foreach (var filter in filterDictionary)
    {
        var fieldName = filter.Key;
        var values = filter.Value;

        if (values.Count > 0)
        {
            q = q.Where(c => values.Contains(c.GetType().GetProperty(fieldName).GetValue(c, null)?.ToString()));
        }
    }

    return q.OrderBy(c => c.ProductTypeName);
}

You can create LINQ queries targeting specific search criteria by dynamically generating WHERE clauses based on user input. This approach provides flexibility and allows easy filtering of data based on user-defined parameters. Note that this code assumes that the value of filterDictionary is List<string>, and that the attribute name of the ProductDetail object is consistent with the key name of filterDictionary. For more robust processing, it is recommended to add exception handling and attribute name verification.

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