Question

Using the DatastoreService how can I do queries for String containing some string similar to Java String:

• contains
• startsWith
• endsWith

Answer 1

When querying against a String property, exact matches are the easiest, since that behavior works “out of the box”.

“startsWith” queries can be done fairly easily by turning property startsWith: abc into property >= 'abc' and property < 'abd', where you calculate the end of the range.

“endsWith” can be done by storing a reversed copy of the String, and creating a query as above, but with the target reversed. I.e., property endsWith: 'abc' becomes `propertyReversed >= ‘cba’ and propertyReversed < ‘cbb’.

“contains” is a large challenge. There are several approaches, and the right one for your situation depends on your situation. If the string is relatively short (e.g., a name of an address), you could store list of trailing substrings, matching against them with a range query as above.