How to Perform Prefix String Searches in Google App Engine Datastore?

Prefix String Search in Google App Engine Datastore

Question:

Can Datastore search for entities whose names begin with a specific string?

Answer:

Yes, it is possible to perform prefix string searches in Datastore.

Details:

Datastore does not support a direct prefix search operator. However, you can achieve this functionality using a combination of inequality filters.

To list entities with names starting with a prefix, you need to specify two filters:

• A filter to select entities greater than or equal to the prefix.
• A filter to select entities less than the next string in lexicographical order after the prefix.

Example:

Suppose you want to search for Places with the "li" prefix. The corresponding query would be:

<code class="go">q = datastore.NewQuery("Places").Filter("Name >=", "li").Filter("Name <", "lj")</code>

This query will return Places with names such as:

liam
lisotto
lizst

But it will exclude names like:

abc
ljoi
lj
qwerty

Note: Capital and lowercase letters are treated differently in lexicographical order. For instance, "List" is less than "li" in lexicographical order.

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